nl80211: Update channel information after channel switch notification

nl80211: Update channel information after channel switch notification

When channel switch happens, driver wrapper's internal channel
information needs to be updated so that the new frequency will be used
in operations using drv->assoc_freq. Previously, only bss->freq was
updated and the new frequency was also indicated in the EVENT_CH_SWITCH
event. This could potentially leave out couple of cases that use
drv->assoc_freq at least as a fallback mechanism for getting the current
operating frequency.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>