net: xdp: don't call notifiers during driver init

Drivers will commonly perform feature setting during init, if they use
the xdp_set_features_flag() helper they'll likely run into an ASSERT_RTNL()
inside call_netdevice_notifiers_info().

Don't call the notifier until the device is actually registered.
Nothing should be tracking the device until its registered and
after its unregistration has started.

Fixes: 4d5ab0ad ("net/mlx5e: take into account device reconfiguration for xdp_features flag")
Link: https://lore.kernel.org/r/20230316220234.598091-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/xdp.c

@@ -781,7 +781,9 @@ void xdp_set_features_flag(struct net_device *dev, xdp_features_t val)
 		return;
 
 	dev->xdp_features = val;
-	call_netdevice_notifiers(NETDEV_XDP_FEAT_CHANGE, dev);
+
+	if (dev->reg_state == NETREG_REGISTERED)
+		call_netdevice_notifiers(NETDEV_XDP_FEAT_CHANGE, dev);
 }
 EXPORT_SYMBOL_GPL(xdp_set_features_flag);