ath9k: Fix basic connectivity issue

This patch temporarily fixes a regression introduced by BT coexistence support.
There is an instability in connection when BT coexistence is enabled on some h/w.
This interim fix introduces a module parameter for BT coexistence configuration.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>