ath10k: wmi: disable softirq's while calling ieee80211_rx

This is done in order not to trig the below warning in
ieee80211_rx_napi:

WARN_ON_ONCE(softirq_count() == 0);

ieee80211_rx_napi requires that softirq's are disabled during
execution.

The High latency bus drivers (SDIO and USB) sometimes call the wmi
ep_rx_complete callback from non softirq context, resulting in a trigger
of the above warning.

Calling ieee80211_rx_ni with softirq's already disabled (e.g., from
softirq context) should be safe as the local_bh_disable and
local_bh_enable functions (called from ieee80211_rx_ni) are fully
reentrant.

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