Stream: detect port absence in proxy_pass with IP literal.

This is a clone of http commit 26c127bab5ef.
diff --git a/src/stream/ngx_stream_upstream.c b/src/stream/ngx_stream_upstream.c
index 805ee70..69dddc5 100644
--- a/src/stream/ngx_stream_upstream.c
+++ b/src/stream/ngx_stream_upstream.c
@@ -388,7 +388,7 @@
     uscf->port = u->port;
     uscf->no_port = u->no_port;
 
-    if (u->naddrs == 1) {
+    if (u->naddrs == 1 && (u->port || u->family == AF_UNIX)) {
         uscf->servers = ngx_array_create(cf->pool, 1,
                                          sizeof(ngx_stream_upstream_server_t));
         if (uscf->servers == NULL) {