bridge: Fix high cpu utilization.

When there are more than one ovs-vswitchd processes started,
only one process is enabled.  The disabled processes should
just sleep.  However, a bug in ovs makes the disabled processes
keep waking up on global connectivity sequence number which is
never sync'ed.  Consequently, those processes use 100% cpu.

This commit fixes the bug by always sync up the connectivity
sequence number for disabled processes.

Reported-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Alex Wang <alexw@nicira.com>
Acked-by: Joe Stringer <joestringer@nicira.com>