BUG/MINOR: checks: Report a socket error before any connection attempt

When a health-check fails, if no connection attempt was performed, a socket
error must be reported. But this was only done if the connection was not
allocated. It must also be done if there is no control layer. Otherwise, a
L7TOUT will be reported instead.

It is possible to not having a control layer for a connection if the connection
address family is invalid or not defined.

This patch must be backported to 2.2.
diff --git a/src/check.c b/src/check.c
index 88c78ed..c281bb2 100644
--- a/src/check.c
+++ b/src/check.c
@@ -655,8 +655,8 @@
 		set_server_check_status(check, HCHK_STATUS_SOCKERR, err_msg);
 	}
 
-	if (!conn) {
-		/* connection allocation error before the connection was established */
+	if (!conn || !conn->ctrl) {
+		/* error before any connection attempt (connection allocation error or no control layer) */
 		set_server_check_status(check, HCHK_STATUS_SOCKERR, err_msg);
 	}
 	else if (conn->flags & CO_FL_WAIT_L4_CONN) {