event/reactor: update last_action for timer pollers

Include timer-based pollers in the active/idle check that uses
last_action to determine when a reactor last executed an action.

Change-Id: Ib8f1253675b57aeb59206d099c6257f6d07f5acf
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>

lib/event/reactor.c

@@ -345,6 +345,7 @@ _spdk_reactor_run(void *arg)
 					poller->state = SPDK_POLLER_STATE_WAITING;
 					spdk_poller_insert_timer(reactor, poller, now);
 				}
+				last_action = spdk_get_ticks();
 			}
 		}