[][kernel][common][hnat][Fix the problem that deleting wifi subinterface fails]

Fix the problem that deleting wifi subinterface fails.
Fix duplication of adding the same subinterface to whnat_interface.

The previous code will fail when encountering the following situations:
1:Add subinterface to whnat_interface and then delete it,
finally, delete the subinterface failed.
2:Add wifi subinterface(eg:rax0.200) to whnat_interface, then rax0 down,
add the same wifi subinterface to whnat_interface through echo command.
there are two identical wifi subinrefaces in whnat_interface.

The patch fix these.


Change-Id: I6ae98fbfc12522cfd6528df81509e5bc30a87e76
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6873054
2 files changed