vswitchd: Fix issue of networking not working when Tools not installed

vswitchd: Fix issue of networking not working when Tools not installed

During the transition to the configuration database, not all code from
the bridge compatibility layer was updated.  In particular, the code
which removes port configuration based on RTNL notifications of port
removal was not updated.  This commit brings that code back.

Note that the code that removes ports based on actively checking whether
ports exist is still commented out pending a review of its impact on GRE
support.

Bug #2370