BUG/MEDIUM: connection: local_send_proxy must wait for connection to establish

The conn_local_send_proxy() function has to retrieve the local and remote
addresses, but the getpeername() and getsockname() functions may fail until
the connection is established. So now we catch this error and poll for write
when this happens.
diff --git a/src/connection.c b/src/connection.c
index 38d4ca6..d882bb7 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -531,14 +531,16 @@
 	if (conn->flags & CO_FL_SOCK_WR_SH)
 		goto out_error;
 
-	/* The target server expects a PROXY line to be sent first. */
+	/* The target server expects a PROXY line to be sent first. Retrieving
+	 * local or remote addresses may fail until the connection is established.
+	 */
 	conn_get_from_addr(conn);
 	if (!(conn->flags & CO_FL_ADDR_FROM_SET))
-		goto out_error;
+		goto out_wait;
 
 	conn_get_to_addr(conn);
 	if (!(conn->flags & CO_FL_ADDR_TO_SET))
-		goto out_error;
+		goto out_wait;
 
 	trash.len = make_proxy_line(trash.str, trash.size, &conn->addr.from, &conn->addr.to);
 	if (!trash.len)