Parallelize bridge_input step 1.8/2:

Parallelize bridge_input step 1.8/2:
Parallelize bridge member interfaces list --
o  Split bridge_iflist into percpu part and shared part (bridge_ifinfo).
   The shared part contains STP related information.
o  Put create bridge_iflist on each CPU and put it onto percpu member
   interface list.
o  All of the STP operation is still serialized by bridge's serializer,
   except testing member interface's STP state.
o  Span interfaces no longer have unused STP information.