ath11k: add tx hw 802.11 encapsulation offloading support

This patch adds support for ethernet rxtx mode to the driver. The feature
is enabled via a new module parameter. If enabled to driver will enable
the feature on a per vif basis if all other requirements were met.

Signed-off-by: Shashidhar Lakkavalli <slakkavalli@datto.com>
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200430152814.18481-1-john@phrozen.org