patch was slightly modified to be applied to openssh-7.2_p2
Original patch:
http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/serverloop.c.diff?r1=1.188&r2=1.189&sortby=date&f=h&f=u

===================================================================
RCS file: /cvs/src/usr.bin/ssh/serverloop.c,v
retrieving revision 1.188
retrieving revision 1.189
diff -u -r1.188 -r1.189
--- a/serverloop.c
+++ b/serverloop.c
@@ -472,7 +472,7 @@
 
 	/* XXX fine grained permissions */
 	if ((options.allow_streamlocal_forwarding & FORWARD_LOCAL) != 0 &&
-	    !no_port_forwarding_flag) {
+	    !no_port_forwarding_flag && use_privsep) {
 		c = channel_connect_to_path(target,
 		    "direct-streamlocal@openssh.com", "direct-streamlocal");
 	} else {
@@ -748,7 +749,7 @@
 
 		/* check permissions */
 		if ((options.allow_streamlocal_forwarding & FORWARD_REMOTE) == 0
-		    || no_port_forwarding_flag) {
+		    || no_port_forwarding_flag || !use_privsep) {
 			success = 0;
 			packet_send_debug("Server has disabled port forwarding.");
 		} else {