Bug 10302 - BGP attribute AIGP (draft-ietf-idr-aigp) not decoded - Fix

Change-Id: Ib8b3c5666932777218e33b74cca33b791c883fc9
Reviewed-on: https://code.wireshark.org/review/3226
Reviewed-by: Evan Huus <eapache@gmail.com>