Replace uses of proto_get_frame_protocols with proto_is_frame_protocol when only one protocol is desired.

Also use proto_get_frame_protocols in main_menubar.c instead of doing it "manually".

Change-Id: Ie7a365c538700f2cebdd1e3d253f2fd9b189f5cf
Reviewed-on: https://code.wireshark.org/review/5851
Reviewed-by: Michael Mann <mmann78@netscape.net>