CLEANUP: stream: Remove bogus loop in conn_si_send_proxy

The if-statement was converted into a while-loop in
7fe45698f58a53dda9182a5970a2ea4bda9f92fe to handle EINTR.

This special handling was later replaced in
0a03c0f022faf2773995fc8b9d14256c8a306e5a by conn_sock_send.

The while-loop was not changed back and is not unconditionally
exited after one iteration, with no `continue` inside the body.

Replace by an if-statement.
diff --git a/src/stream_interface.c b/src/stream_interface.c
index 669a906..e9fe00f 100644
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -339,7 +339,7 @@
 	 * connection, in which case the connection is validated only once
 	 * we've sent the whole proxy line. Otherwise we use connect().
 	 */
-	while (conn->send_proxy_ofs) {
+	if (conn->send_proxy_ofs) {
 		const struct conn_stream *cs;
 		int ret;
 
@@ -399,7 +399,6 @@
 			goto out_wait;
 
 		/* OK we've sent the whole line, we're connected */
-		break;
 	}
 
 	/* The connection is ready now, simply return and let the connection