bridge: Reconfigure in single pass.

This greatly simplifies the reconfiguration code, making it much easier
to understand and modify.  The old multi-pass configuration had the
property that it didn't delay block packet processing as much, but that's
not much of a worry anymore now that latency critical activities have
been moved outside the main thread.

Signed-off-by: Ben Pfaff <blp@nicira.com>
bridge: Support changing port numbers.

Feature #21293.
Requested-by: Anuprem Chalvadi <achalvadi@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>