proto.h; (try to) fix bug in DISSECTOR_ASSERT_CMP... macros;

 Also: re-enable use of DISSECTOR_ASSERT_CMP... macros in packet-ceph.c

Change-Id: Icee80381f5c8feb14cfc7e4033bdeb893018ce95
Reviewed-on: https://code.wireshark.org/review/3749
Reviewed-by: Bill Meier <wmeier@newsguy.com>