If non-zero, this is the unique service number which
unconfigured Bridging Virtual Circuits are added to
if frxPortDefaultBridgingVLAN is non zero (set to a
VLAN ID) and frxPortDefaultBridgingGrouping
is set to groupVCsIntoOneVport. This allows an unconfigured
VC to be added to an existing configured bridging service
virtual circuit group.
If zero, then unconfigured VCs will be added to a newly
created (dynamic) Briding Service instance (i.e. a new
virtual port is created dynamically).