Add dissection of IS-IS Router CAPABILITY TLV.
Bug 10520.

Change-Id: I8d8d56e36d90088af3cd7d2490f95c5f87c75423
Reviewed-on: https://code.wireshark.org/review/4420
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>