airoha: backport kernel part of WiFi MT76 offload patch

airoha: backport kernel part of WiFi MT76 offload patch

Backport the kernel parf of the WiFi MT76 offload patch. This is needed
as we have a dedicated package that only have mt76 related changes.

Add missing include in airoha_offload.h in order to enable MT76 NPU
offloading (and fix compilation error)

Signed-off-by: Lorenzo Bianconi <[email protected]>
[ improve commit title/description and use proper patch ]
Link: https://github.com/openwrt/openwrt/pull/20807
Signed-off-by: Christian Marangi <[email protected]>