CP2179: Fix warning: no previous prototype for proto_register_cp2179 [-Wmissing-prototypes]

Move on top also prototype of proto_reg_handoff_cp2179

Change-Id: I00f23a88606426acd17d63104630a885682d3c02
Reviewed-on: https://code.wireshark.org/review/4452
Reviewed-by: Anders Broman <a.broman58@gmail.com>