ath6kl: Move and rename ath6kl_cleanup_vif function

Rename ath6kl_cleanup_vif function as 'ath6kl_cfg80211_vif_stop'
which is the more appropriate name considering the functionality
of the module and vif specific cleanup is actually done by
ath6kl_cfg80211_vif_cleanup. Also move it to cfg80211.c.
Also make ath6kl_cfg80211_sta_bmiss_enhance as static function.
This addresses a FIXME/TODO.

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath6kl/cfg80211.h

@@ -61,7 +61,5 @@ void ath6kl_cfg80211_cleanup(struct ath6kl *ar);
 
 struct ath6kl *ath6kl_cfg80211_create(void);
 void ath6kl_cfg80211_destroy(struct ath6kl *ar);
-/* TODO: remove this once ath6kl_vif_cleanup() is moved to cfg80211.c */
-void ath6kl_cfg80211_sta_bmiss_enhance(struct ath6kl_vif *vif, bool enable);
 
 #endif /* ATH6KL_CFG80211_H */