ath10k: do not setup rts/frag thresholds for suspended interfaces

mac80211 calls for rts/frag threshold hooks before
any interface is brought back up again when
resuming.

We would set vdev parameters before given vdev is
created lading to a FW crash.

rts/frag thresholds will be re-set accordingly in
add_interface() hook anyway.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>