core: signal parent-active only when the parent AC is activated

The parent-active signal is used by the manager to determine when the
parent active-connection is ready and a connection that depend on it
can proceed.

The AC state could transition from ACTIVATING directly to
DEACTIVATING; in such case we should not emit the signal but instead
just stop watching the parent AC.

Fixes: 6e382ea91d ('active-connection: add parent active connection tracking')
https://bugzilla.redhat.com/show_bug.cgi?id=1778073
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/510

src/nm-active-connection.c

@@ -996,6 +996,8 @@ parent_state_cb (NMActiveConnection *parent_ac,
 		return;
 
 	unwatch_parent (self, TRUE);
+
+	if (parent_state == NM_ACTIVE_CONNECTION_STATE_ACTIVATED)
 		g_signal_emit (self, signals[PARENT_ACTIVE], 0, parent_ac);
 }