Backporting CVE-2020-3702 ath9k patches to stable

Hello! I would like to request for backporting following ath9k commits
which are fixing CVE-2020-3702 issue.

56c5485c9e44 ("ath: Use safer key clearing with key cache entries")
73488cb2fa3b ("ath9k: Clear key cache explicitly on disabling hardware")
d2d3e36498dd ("ath: Export ath_hw_keysetmac()")
144cd24dbc36 ("ath: Modify ath_key_delete() to not need full key entry")
ca2848022c12 ("ath9k: Postpone key cache entry deletion for TXQ frames reference it")

See also:
https://lore.kernel.org/linux-wireless/87o8hvlx5g.fsf@codeaurora.org/ (local)

This CVE-2020-3702 issue affects ath9k driver in stable kernel versions.
And due to this issue Qualcomm suggests to not use open source ath9k
driver and instead to use their proprietary driver which do not have
this issue.

Details about CVE-2020-3702 are described on the ESET blog post:
https://www.welivesecurity.com/2020/08/06/beyond-kr00k-even-more-wifi-chips-vulnerable-eavesdropping/

Two months ago ESET tested above mentioned commits applied on top of
4.14 stable tree and confirmed that issue cannot be reproduced anymore
with those patches. Commits were applied cleanly on top of 4.14 stable
tree without need to do any modification.