[PMTUd] if PMTUd is rescheduled, then enforce a new run

the usleep between each PMTUd run will give time to the other threads to grab the wrlock

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

libknet/threads_common.c

@@ -45,6 +45,7 @@ static int pmtud_reschedule(knet_handle_t knet_h)
 	}
 
 	knet_h->pmtud_abort = 1;
+	knet_h->pmtud_forcerun = 1;
 
 	if (knet_h->pmtud_waiting) {
 		pthread_cond_signal(&knet_h->pmtud_cond);