ath9k: merge another round of upstream (or -pending) fixes and cleanups

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39138 3c298f89-4303-0410-b956-a3cf2f4a3e73
ar71xx: add missing tx gain table flag for buffalo wzr-hp-g450h

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39139 3c298f89-4303-0410-b956-a3cf2f4a3e73