Add dissector for Great Britain Companion Specification (GBCS)

The Smart Metering Equipment Technical Specifications (SMETS) requires
that Gas Smart Metering Equipment (GSME), and Electricity Smart
Metering Equipment (ESME) including variants, meet the requirements
described in the Great Britain Companion Specification (GBCS).

GBCS messages are end-to-end and contains ZigBee, DLMS or ASN.1
formatted payloads. The GBCS messages are transported via IPor via
the ZigBee Tunneling cluster.

https://smartenergycodecompany.co.uk/document-download-centre/download-info/gbcs-v2-1/

Bug: 15381
Change-Id: I28ca9831fc266a6abd310db103306b98786e63f9
Reviewed-on: https://code.wireshark.org/review/31168
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Reviewed-by: Martin Boye Petersen <martinboyepetersen@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

docbook/release-notes.asciidoc

@@ -106,6 +106,7 @@ DXL
 E1AP (5G)
 EVS (3GPP TS 26.445 A.2 EVS RTP)
 Exablaze trailers
+Great Britain Companion Specification (GBCS) used in the Smart Metering Equipment Technical Specifications (SMETS)
 General Circuit Services Notification Application Protocol (GCSNA)
 GeoNetworking (GeoNw)
 GLOW Lawo Emberplus Data format

epan/dissectors/CMakeLists.txt

@@ -1034,6 +1034,7 @@ set(DISSECTOR_SRC
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-fw1.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-g723.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gadu-gadu.c
+	${CMAKE_CURRENT_SOURCE_DIR}/packet-gbcs.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gcsna.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gdb.c
 	${CMAKE_CURRENT_SOURCE_DIR}/packet-gdsdb.c