bgpd: Fix for commit 6a4677b7, fixes BZ#729

  The timers are rearmed after events processing. After 6a4677b7 we
do not generate events that can rearm the holdtime timer.

  Fix it's to call bgp_timer_set() directly as it's done from bgp_event().

Signed-off-by: Jorge Boncompte [DTI2] <jorge@dti2.net>
Tested-by: Martin Winter <mwinter@opensourcerouting.org>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/bgpd/bgp_packet.c b/bgpd/bgp_packet.c
index 024f5e7..2d62c8d 100644
--- a/bgpd/bgp_packet.c
+++ b/bgpd/bgp_packet.c
@@ -1854,8 +1854,9 @@
   peer->update_in++;
   peer->update_time = bgp_clock ();
 
-  /* Cancel holdtime timer */
+  /* Rearm holdtime timer */
   BGP_TIMER_OFF (peer->t_holdtime);
+  bgp_timer_set (peer);
 
   return 0;
 }