Don't swallow unrecognized link handles

[jhendrixMSFT]

Per spec section 2.8.17, the session must be terminated.

Fixes https://github.com/Azure/go-amqp/issues/182

[jhendrixMSFT]

This has highlighted a potential deadlock in the error handling for session mux. In this case, the mux first receives a mismatched attach frame, so it shoves an &Error{} into the s.close channel. On the next iteration, the select on s.close and s.rx choses s.rx which reads yet another invalid frame. Unfortunately, s.close is full so the mux hangs.