L2CAP: Rename classic facade and minor refactor

* Add classic annotation to L2CAP classic facades and cert classes so
  that we can make LE ones later
* Add ToString method to le::internal::Link and classic::internal::Link
* AclConnection should have a default address type of PUBLIC

Bug: 140938432
Test: make, cert test
Change-Id: I4d7bb31a82805e60af17fe25c99c0ef783c9bee3