core: signal property changes for IpMethod

If the modem's IP Method changes after construction because the
modem's full capabilities were only discovered after it was created,
make sure the change notification gets emitted.

src/mm-modem-base.c

@@ -626,6 +626,10 @@ mm_modem_base_init (MMModemBase *self)
                                                     MM_MODEM_UNLOCK_RETRIES,
                                                     NULL,
                                                     MM_MODEM_DBUS_INTERFACE);
+    mm_properties_changed_signal_register_property (G_OBJECT (self),
+                                                    MM_MODEM_IP_METHOD,
+                                                    NULL,
+                                                    MM_MODEM_DBUS_INTERFACE);
 }
 
 static void