wlan: Notify upper layer about channel change after CSA is done

Currently channel change info is not being reflected in
iw wlan0 link or in wpa_cli. This change updates the flow
in eCSR_ROAM_STA_CHANNEL_SWITCH where it updates about the
channel change info after Channel Switch Announcement is
processed in case of sta using cfg80211_ch_switch_notify.

Change-Id: I3cab261506ca5f6c1922fe9c6b06f4964cdee4cc
CRs-Fixed: 2769278