ath9k_htc: Do not support PowerSave by default

ath9k_htc: Do not support PowerSave by default

commit 6bca610d97b6139a1d7598b8009da9d339daa50f upstream.

It is a copy/paste of patch provided by Sujith for ath9k.

"Even though we make sure PowerSave is not enabled by default
by disabling the flag, WIPHY_FLAG_PS_ON_BY_DEFAULT on init,
PS could be enabled by userspace based on various factors
like battery usage etc. Since PS in ath9k is just broken
and has been untested for years, remove support for it, but
allow a user to explicitly enable it using a module parameter."

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>