BUG/MEDIUM: peers: stop considering ack messages teaching a full resync

The re-con cursor was updated receiving any ack message
even if we are pushing a complete resync to a peer. This cursor
is reset at the end of the resync but if the connection is broken
during resync, we could re-start at an unwanted point.

With this patch, the peer stops to consider ack messages pushing
a resync since the resync process has is own acknowlegement and
is always restarted from the beginning in case of broken connection.

This patch should be backported on all supported branches ( >= 1.6 )

(cherry picked from commit b0d60bed36cfbfead5a35e6a9520e8d5e9345a7f)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/peers.c b/src/peers.c
index f12b90b..d23a1fd 100644
--- a/src/peers.c
+++ b/src/peers.c
@@ -1807,6 +1807,10 @@
 	uint32_t update;
 	struct shared_table *st;
 
+	/* ignore ack during teaching process */
+	if (p->flags & PEER_F_TEACH_PROCESS)
+		return 1;
+
 	table_id = intdecode(msg_cur, msg_end);
 	if (!*msg_cur || (*msg_cur + sizeof(update) > msg_end)) {
 		/* malformed message */