connmgr: Fix attempt to take mutex recursively when exiting fail-open.

connmgr: Fix attempt to take mutex recursively when exiting fail-open.

If one configured a controller which does not exist, waited for the switch
to enter fail-open mode, and then deleted the controller, then
ofproto_set_controllers() would take ofproto_mutex and call
update_fail_open(), which would call fail_open_destroy(), which would call
fail_open_recover(), which would call ofproto_delete_flow(), which requires
ofproto_mutex not to be held since it eventually try to take it.  This
caused OVS to abort.

This fixes the problem by releasing ofproto_mutex earlier, since nothing
seems to require it being held so long (a comment in
connmgr_set_controllers() says that this is likely to be the case).

Better annotations would have found this problem at compile time.  A later
patch adds them.

Reported-by: ZhengLingyun <konghuarukhr@163.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>