MEDIUM: checks: enable the PROXY protocol with health checks

When health checks are configured on a server which has the send-proxy
directive and no "port" nor "addr" settings, the health check connections
will automatically use the PROXY protocol. If "port" or "addr" are set,
the "check-send-proxy" directive may be used to force the protocol.
diff --git a/src/checks.c b/src/checks.c
index 52f70d2..7895e5d 100644
--- a/src/checks.c
+++ b/src/checks.c
@@ -1331,6 +1331,8 @@
 		 */
 		ret = s->check.proto->connect(conn, 1);
 		conn->flags |= CO_FL_WAKE_DATA;
+		if (s->check.send_proxy)
+			conn->flags |= CO_FL_LOCAL_SPROXY;
 
 		switch (ret) {
 		case SN_ERR_NONE: