wifi: mt76: add missing locking to protect against concurrent rx/status calls

commit 5b8ccdfb upstream.

According to the documentation, ieee80211_rx_list must not run concurrently
with ieee80211_tx_status (or its variants).

Cc: stable@vger.kernel.org
Fixes: 88046b2c ("mt76: add support for reporting tx status with skb")
Reported-by: Brian Coverstone <brian@mainsequence.net>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>