ath6kl: Delay initial group key setup in AP mode

The target is not ready to accept addkey commands until the connect
event has been delivered, so delay these operations for the initial GTK.
In addition, properly set interface connected and mark netdev ready when
the AP mode setup has been completed.

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