Disable Nagle's algorithm on the backend as well

Fixes #2134.

lib/libvarnish/vtcp.c

@@ -279,6 +279,7 @@ VTCP_connect(const struct suckaddr *name, int msec)
 	struct pollfd fds[1];
 	const struct sockaddr *sa;
 	socklen_t sl;
+	int val;
 
 	if (name == NULL)
 		return (-1);
@@ -296,6 +297,9 @@ VTCP_connect(const struct suckaddr *name, int msec)
 	if (msec != 0)
 		(void)VTCP_nonblocking(s);
 
+	val = 1;
+	AZ(setsockopt(s, IPPROTO_TCP, TCP_NODELAY, &val, sizeof val));
+
 	i = connect(s, sa, sl);
 	if (i == 0)
 		return (s);