use supported/unsupported for the bitfield elements
order them from MSB to LSB

Change-Id: Ie758285c2cf5d19e00d6d256c49acca15ce81168
Reviewed-on: https://code.wireshark.org/review/4746
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Martin Kaiser <wireshark@kaiser.cx>