Consider templatizing the net_entity container in the net_ip class

[cliffg-softwarelibre]

Currently the container inside the net_ip class is a std::vector, which is a good default. However, some applications may wish to use a different container, or may wish to use statically allocated memory instead of a dynamic sized container (e.g. in a small embedded environment).

The container type could be a template parameter on the class (changing net_ip into a class template instead of a regular class).

This issue is similar to the other Chops Net IP issues where we are providing more flexibility in the container and buffer types.