Track and cache bridge and port MAC addresses.

Track and cache bridge and port MAC addresses.

   Check for MAC address change when we get notifications.
   If we get a port notification and find that the port MAC address
   changed, we check if the bridge MAC address changed as well.
   This will be useful for modifying RSTPLIB to allow setting bridge
   address instead of trying to replicate the kernel bridge address
   computation.

Signed-off-by: Srinivas Aji <Aji_Srinivas@emc.com>