[][Add hnat entry index sanity check]

[Description]
Add sanity check for hnat entry index

[Release-log]
N/A

Change-Id: I6826a8449c311e8304b0bb09d51ae594a6d115b3
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4734416
1 file changed