Introduced SCM_CREDENTIALS / SCM_CREDS in the socket control msgs.

src/nxt_port_rpc.c

@@ -393,8 +393,8 @@ nxt_port_rpc_remove_peer(nxt_task_t *task, nxt_port_t *port, nxt_pid_t peer)
     msg.fd[1] = -1;
     msg.buf = &buf;
     msg.port = port;
-
-    msg.port_msg.pid = peer;
+    msg.u.removed_pid = peer;
+    msg.port_msg.pid = nxt_pid;
     msg.port_msg.type = _NXT_PORT_MSG_REMOVE_PID;
 
     peer_link = lhq.value;