[][MAC80211][misc][Add MT7996 external openwrt build]

[Description]
Add MT7996 external openwrt build

[Release-log]
N/A

Change-Id: I92f3abce893f401df64f7390f1783d4557963848
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/6967021
16 files changed