qtnfmac: keeping track of "generation" for STA info

Keep generation in per-VIF data structure and increment it whenever STA
list is changed. Use generation value to fill struct station_info when
required.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>