qtnfmac: move current channel info from vif to mac

Wireless cfg80211 core supplies channel settings in cfg80211_ap_settings
structure for each BSS in multiple BSS configuration. On the other hand
all the virtual interfaces on one radio are using the same PHY settings
including channel.

Move chandef structure from vif to mac structure in order to mantain
the only instance of cfg80211_chan_def structure in qtnf_wmac
rather than its multiple copies in qtnf_vif.

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>