proxy: Turn on TCP_NODELAY for the proxy->upstream leg

Nagle doesn't actually affect us too badly here, as we don't write
the header and then the data in two separate calls under normal
circumstances, which is the pathological case, but we should have
NODELAY on, regardless

src/proxy/proxy.c

@@ -186,6 +186,13 @@ void proxy_finish_connect_to_upstream( struct proxier *proxy, off64_t size ) {
 	}
 
 	proxy->upstream_size = size;
+
+	if ( AF_UNIX != proxy->connect_to.family ) {
+		if ( sock_set_tcp_nodelay( proxy->upstream_fd, 1 ) == -1 ) {
+			warn( SHOW_ERRNO( "Failed to set TCP_NODELAY" ) );
+		}
+	}
+
 	info( "Connected to upstream on fd %i", proxy->upstream_fd );
 
 	return;