qtnfmac: implement reporting current channel

Implement current channel reporting functionality. Current operating
channel can be obtained either directly using cfg80211 get_channel
callback or from stats reported by cfg80211 survey_dump callback.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Avinash Patil <avinashp@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>