The MAC address of the station authorized to be
on this port. This address could either have been
configured by specifying a regular station address
for hubSecPtSecurityAddress, or it could have been
learned by the agent if hubSecPtSecurityAddress
was set to one of the special values listed above.
Once the agent has learned an authorized address,
it will be saved across powerfails, unless the
agent was configured for learnContinuous mode.