Indicates the MAC's optional bridging functions.
The Value -1 is used to indicate that bridging is
not supported by this MAC.
The value is a sum. This value initially takes
the value zero, then for each function present, 2
raised to a power is added to the sum. The powers
are according to the following table:
Function Power
tb 0 -- Transparent bridging active
sr 1 -- Src routing active
srt 2 -- Src routing transparent active