Make EscrowPacketFee private

[colin-axner]

Summary

We should move the IsFeeEnabled check to the message server and make EscrowPacketFee private. This makes the message MsgPayPacketFee and MsgPayPacketFeeAsync the only entry points to this function.

I noticed this might be a better approach while adding an IsLocked() check. I think it makes sense to remove security checks from EscrowPacketFee and have that function simply escrow the packet fee.

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged/assigned

[damiannolan]

Seems like EscrowPacketFee is used extensively throughout the tests. We may be able to work around it by setting fees in store manually, as that appears to be the general purpose in most test cases.