[frr]: upgrade frr to frr-7.5-s2 tag

[lguohan]

Signed-off-by: Guohan Lu lguohan@gmail.com

- Why I did it
Fix #5929
pick-up upstream fixes. important ones

• bgpd: Removing "neighbor allowas-in"

complete lists

*   6b2b5cce3 2021-01-29 | Merge pull request #7977 from ton31337/fix/allowas_in_reset_value_7.5 (HEAD -> frr/7.5, tag: frr-7.5-s2, upstream/stable/7.5, origin/frr/7.5, stable/7.5) [Donald Sharp]
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| * f403534df 2021-01-28 | bgpd: Removing "neighbor <peer-group> allowas-in" [Kishore Kunal]
* |   86e2f106c 2021-01-28 | Merge pull request #7962 from ton31337/fix/bgpd_validate_community_7.5 [Donald Sharp]
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| * e182af45c 2021-01-05 | bgpd: separate lcommunity validation from tokenizer [Wesley Coakley]
| * 2cf37d594 2020-12-30 | bgpd: Validate community list if they are not malformed [Donatas Abraitis]
|/
*   a4af08a19 2021-01-22 | Merge pull request #7912 from idryzhov/7.5-backports-2021-01 [Donald Sharp]
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| * 160021013 2021-01-12 | bgpd : multiple memory leak fixes in show commands [Sarita Patra]
| * 46a2b560f 2021-01-19 | tools: fix frr-reload BFD profile support [Rafael Zalamena]
| * 7f6c81fca 2020-12-02 | ospfd: fix area removal at interface level [ckishimo]
| * f7db4dfb1 2021-01-08 | bfdd: update vrf of received packet [Philippe Guibert]
| * 4d470f3ef 2021-01-08 | bfdd: enable bfd session if vrf interface available [Philippe Guibert]
| * c656985fb 2021-01-08 | bfdd: socket should be bound to vrf interface by default [Philippe Guibert]
| * f30c002b8 2021-01-15 | bgpd: Allow peer-groups to have `ttl-security hops` configured [Donald Sharp]
| * 85ff76513 2021-01-15 | configure.ac: Correct library name for sysrepo [Bo Zhang]
| * d00c543f1 2020-12-04 | bgpd: Handle IPv6 prefixes with IPv4 nexthops for zebra [Donatas Abraitis]
| * 87b9b2973 2021-01-06 | zebra: zebra route-map delay-timer is global not per vrf [Donald Sharp]
| * 91e1adec9 2021-01-05 | bgpd: Fix default-originate clearing from peer-groups. [zyxwvu Shi]
| * 0f2f32fa1 2021-01-05 | isisd: When last area address is removed, resign if we were DR [Karen Schoener]
| * 842e99d49 2021-01-02 | vrrpd.yang bug fix: modify augment path to comply with rfc 7950 [Bo Zhang]
| * 9616ef937 2020-12-24 | ospfd: fix no show database output when selecting vrf [Louis Scalbert]
| * 4c4764e36 2020-11-30 | ospf6d: ospfv3 disable on the interface, but interface prefix still shown in the output [Yash Ranjan]
| * 1870dbd86 2020-12-14 | ospf6d: Link LSA is not updated when router priority is modified [Mobashshera Rasool]
| * 4883a06c3 2020-12-10 | bgpd: fix evpn route-map vni filter at origin [Chirag Shah]
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*   9c087052a 2021-01-15 | Merge pull request #7877 from vishaldhingra/static_7_5 [Mark Stapp]
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| * a687b6b27 2021-01-15 | staticd: Backend cofiguration code to fix table-id problem [vdhingra]
| * 52370b494 2021-01-15 | staticd: autogenerated code modifications due to yang changes [vdhingra]
| * f9d6511f2 2021-01-15 | staticd: make table-id as the key for path-list [vdhingra]
|/

- How I did it

- How to verify it

- Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006
• 202012

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[lguohan]

lgh@54edb99ee27f:/var/src/sonic-mgmt/tests$ ./run_tests.sh -i veos_vtb -d vlab-02 -n vms-kvm-t1-lag -f vtestbed.csv -k debug -l warning -m individual -q 1 -a False -e --disable_loganalyzer -u -c bgp/test_bgp_bbr.py  === Running tests individually ===
/usr/local/lib/python2.7/dist-packages/ansible/parsing/vault/__init__.py:44: CryptographyDeprecationWarning: Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in a future release.
  from cryptography.exceptions import InvalidSignature
================================================================================================= test session starts ==================================================================================================
platform linux2 -- Python 2.7.17, pytest-4.6.5, py-1.9.0, pluggy-0.13.1
ansible: 2.8.12
rootdir: /var/src/sonic-mgmt/tests, inifile: pytest.ini
plugins: forked-1.3.0, xdist-1.28.0, metadata-1.10.0, html-1.22.1, repeat-0.8.0, ansible-2.2.2
collected 3 items                                                                                                                                                                                                      

bgp/test_bgp_bbr.py::test_bbr_enabled_dut_asn_in_aspath PASSED                                                                                                                                                   [ 33%]
bgp/test_bgp_bbr.py::test_bbr_enabled_dual_dut_asn_in_aspath PASSED                                                                                                                                              [ 66%]
bgp/test_bgp_bbr.py::test_bbr_disabled_dut_asn_in_aspath PASSED                                                                                                                                                  [100%]

----------------------------------------------------------------------- generated xml file: /var/src/sonic-mgmt/tests/logs/bgp/test_bgp_bbr.xml ------------------------------------------------------------------------
============================================================================================== 3 passed in 124.89 seconds ==============================================================================================