Almost all the DMA issues which have plagued ath9k (in station mode)
for years are related to PS. Disabling PS usually "fixes" the user's
connection stablility. Reports of DMA problems are still trickling in
and are sitting in the kernel bugzilla. Until the PS code in ath9k is
given a thorough review, disbale it by default. The slight increase
in chip power consumption is a small price to pay for improved link
stability.

Cc: stable@vger.kernel.org
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>