BUG/MEDIUM: peers: reset commitupdate value in new conns

The commitupdate value of the table is used to check if the update
is still pending for a push for all peers. To be sure to not miss a
push we reset it just after a handshake success.

This patch should be backported on all supported branches ( >= 1.6 )
diff --git a/src/peers.c b/src/peers.c
index b473a4c..16a2fdb 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -2409,6 +2409,8 @@
 		if ((int)(st->table->localupdate - st->update) < 0)
 			st->update = st->table->localupdate + (2147483648U);
 		st->teaching_origin = st->last_pushed = st->update;
+		if ((int)(st->last_pushed - st->table->commitupdate) > 0)
+			st->table->commitupdate = st->last_pushed;
 		HA_SPIN_UNLOCK(STK_TABLE_LOCK, &st->table->lock);
 	}
 
@@ -2459,6 +2461,8 @@
 		if ((int)(st->table->localupdate - st->update) < 0)
 			st->update = st->table->localupdate + (2147483648U);
 		st->teaching_origin = st->last_pushed = st->update;
+		if ((int)(st->last_pushed - st->table->commitupdate) > 0)
+			st->table->commitupdate = st->last_pushed;
 		HA_SPIN_UNLOCK(STK_TABLE_LOCK, &st->table->lock);
 	}