[BRIDGE]: need to ref count the LLC sap

Bridge will OOPS on removal if other application has the SAP open.
The bridge SAP might be shared with other usages, so need
to do reference counting on module removal rather than explicit
close/delete.

Since packet might arrive after or during removal, need to clear
the receive function handle, so LLC only hands it to user (if any).

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>