ath6kl: Make sure to allocate rx buffers after the endpoint connection

Rx buffers should be allocated for control and best effort endpoints only
after the enpoints connection is esablished. But this is done before the
endpoint connection is complete, we don't even the control and BE endpoints
that time. Move the buffer allocation after endpoint connection is over,
after ath6kl_init_hw_start(). Found in review, never seen any real issue
with this.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>