libtls: Don't send TLS close notifies in EAP after application succeeds

libtls: Don't send TLS close notifies in EAP after application succeeds

With the introduction of PT-TLS, we started sending TLS close notifies after
the application layer completes (7bbf7aa9). While this makes sense for TCP based
transports, it is not required in EAP methods. In EAP, handshake completion
can be directly signaled using the outer EAP-SUCCESS message. This also saves
one round-trip in the EAP exchange.

Windows 7/8 does not seem to like TLS close notifies at all in EAP, and either
stalls (EAP-TTLS) or disconnects (PEAP).

Fixes #556.