ofctrl: Wakeup when entering S_UPDATE_FLOWS.

In theory it is possible that ovn-controller tried to install flows by
calling ofctrl_put() while ofctrl is at a state other than
S_UPDATE_FLOWS thus not able to install. So, when entering S_UPDATE_FLOWS,
we should immediately wakeup the main loop so that any pending flows
can be installed without being delayed.

Signed-off-by: Han Zhou <hzhou@ovn.org>
Acked-by: Mark Michelson <mmichels@redhat.com>
(cherry picked from commit fbb8e19)
Signed-off-by: Numan Siddique <numans@ovn.org>

controller/ofctrl.c

@@ -669,6 +669,10 @@ run_S_CLEAR_FLOWS(void)
     }
 
     state = S_UPDATE_FLOWS;
+
+    /* Give a chance for the main loop to call ofctrl_put() in case there were
+     * pending flows waiting ofctrl state change to S_UPDATE_FLOWS. */
+    poll_immediate_wake();
 }
 
 static void