Fix TRILL LSP display issues

1) Sub-TLVs unknown to wireshark are not necessarily invalid
2) Properly show Root Bridge ID
3) Unify Nickname format to HEX_DEC

Change-Id: Ib62f2e2a23f27221b303eaf544868746f56ff6df
Reviewed-on: https://code.wireshark.org/review/3686
Reviewed-by: Anders Broman <a.broman58@gmail.com>