kernel - Major bridging functionality added (bug fixes 4)

kernel - Major bridging functionality added (bug fixes 4)

* Fix an issue where we were assuming that a root bridge receiving a
  configuration packet from a remote bridge would get a path cost
  that already include the root bridge's path cost for that port.
  In fact the target bridge only includes an aggregate path cost to
  root (typically the lowest path cost of all the target bridge's
  ports), which is a fixed value.

* The root bridge must add the local path cost back in.