Fixed C++ style comment

Change-Id: Ife56bb2849b4384c8ea6af3b3913b1a0fbe9ff9e
Reviewed-on: https://code.wireshark.org/review/3160
Petri-Dish: Graham Bloice <graham.bloice@trihedral.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Graham Bloice <graham.bloice@trihedral.com>