ath11k: Don't check arvif->is_started before sending management frames

Commit 66307ca0 ("ath11k: fix mgmt_tx_wmi cmd sent to FW for
deleted vdev") wants both of below two conditions are true before
sending management frames:

1: ar->allocated_vdev_map & (1LL << arvif->vdev_id)
2: arvif->is_started

Actually the second one is not necessary because with the first one
we can make sure the vdev is present.

Also use ar->conf_mutex to synchronize vdev delete and mgmt. TX.

This issue is found in case of Passpoint scenario where ath11k
needs to send action frames before vdev is started.

Fix it by removing the second condition.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1

Fixes: 66307ca0

 ("ath11k: fix mgmt_tx_wmi cmd sent to FW for deleted vdev")
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220506013614.1580274-3-quic_bqiang@quicinc.com