wifi: ath12k: Block radio bring-up in FTM mode

wifi: ath12k: Block radio bring-up in FTM mode

Ensure that all radios remain down when the driver operates in Factory
Test Mode (FTM). Reject any userspace attempts to bring up an
interface in this mode.

Currently, the driver allows userspace to bring up the interface even
though it operates in FTM mode, which violates FTM constraints and
leads to FTM command failures.

Hence, block the radio start when the driver is in FTM mode. Also,
remove ath12k_ftm_mode check from ath12k_drain_tx() because FTM mode
check is already handled in the caller function
(ath12k_mac_op_start()).

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.4.1-00199-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Fixes: 3bc374cbc49e ("wifi: ath12k: add factory test mode support")
Signed-off-by: Aaradhana Sahu <aaradhana.sahu@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250630031502.8902-1-aaradhana.sahu@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>