Second try at the bridge driver module handling cleanup...

1) Eliminate keeping a seperate bridge_list and use a bit on
   the priv_flags structure.  This is equivalent to how the VLAN
   code works. Makes code cleaner and correctly handles cases like
   creating a bridge with the same name as an existing ether device etc.

2) Don't do own module ref counting that is inhernently racy.
   Instead set owner field and cleanup debris on unload.

3) Do last state cleanup in destructor

4) Change of bridge state (dev_open/stop) should use write_lock

5) Make sure timer is not running when cleared.

6) Use "const char *" where possible