Fix TRILL ISIS Hellos:
- MT Port Capability TLVs are present in L1 Hellos
- unify texts

Change-Id: I3dade81ad4487620a8e46e0b242bbbffbb6c2d49
Reviewed-on: https://code.wireshark.org/review/3659
Reviewed-by: Evan Huus <eapache@gmail.com>