ath9k: dfs use CFG80211_CERTIFICATION_ONUS flag

Use CFG80211_CERTIFICATION_ONUS flag in the DFS
detector code. This is required as a preparation
for moving DFS detector code from ath9k to ath
module.

Signed-off-by: Janusz Dziedzic <janusz.dziedzic@tieto.com>
Reviewed-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>