wcn36xx: handle connection loss indication

Firmware sends delete_sta_context_ind when it detects the AP has gone
away in STA mode. Right now the handler for that indication only handles
AP mode; fix it to also handle STA mode.

Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Li <benl@squareup.com>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210901180606.11686-1-benl@squareup.com