ath10k: htt: High latency RX support

Special HTT RX handling for high latency interfaces.

Since no DMA physical addresses are used in the RX ring
config message (this is not supported by the high latency
devices), no RX ring is allocated.
All RX skb's are allocated by the driver and passed directly
to mac80211 in the HTT RX indication handler.

A nice side effect of this is that no huge buffer will be
allocated with dma_alloc_coherent. On embedded systems with
limited memory resources, the allocation of the RX ring is
prone to fail.

Some tweaks made to "make it work":

Removal of protected bit in 802.11 header frame control field.
The chipset seems to do hw decryption but the frame_control
protected bit is still set.

This is necessary for mac80211 not to drop the frame.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>