Some APs advertise that they may be HT40 capable in the capabilites
but the current operating channel configuration may be only HT20.
This causes disconnection as ath9k_htc sets WLAN_RC_40_FLAG despite
the AP operating in HT20 mode.
Hence set this flag only if the current channel configuration
is HT40 enabled.

Cc: stable@kernel.org
Signed-off-by: Vivek Natarajan <vnatarajan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>