[][Fix judgment of NETDEV_UNREGISTER in nf_hnat_netdevice_event]

[Description]
Fix judgment of NETDEV_UNREGISTER in nf_hnat_netdevice_event.
The previous code caused dev_put exception due to unreasonable judgment in nf_hnat_netdevice_event.
For example: when create eth1.1, then delete eth1.1 cause crash.
The change fix it.

[Release-log]
N/A

Change-Id: I844cefca3c1af16e30c8d61bde7e16b5c982f507
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5469830
1 file changed