ath9k: always issue a full hw reset after waking up from full-sleep mode

After waking up from full sleep, registers are accessible, but rx/tx
typically fails. A fast channel change will not recover from this, so
ensure that a full-sleep -> wake transition is always followed by a full
reset.

The reason why this hasn't created any serious problems yet is that it's
hidden by the (wrong) behavior of enabling/disabling the radio when the
wiphy idle state changes.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>