exec: close stdout and stderr streams on child signal

This prevents timing out ubus call when the child invokes further detached
childs inheriting stdio descriptors.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

exec.c

@@ -175,6 +175,12 @@ rpc_exec_process_cb(struct uloop_process *p, int stat)
 
 	ustream_poll(&c->opipe.stream);
 	ustream_poll(&c->epipe.stream);
+
+	close(c->opipe.fd.fd);
+	close(c->epipe.fd.fd);
+
+	ustream_poll(&c->opipe.stream);
+	ustream_poll(&c->epipe.stream);
 }
 
 static void