AZL-110726

In the Linux kernel, the following vulnerability has been resolved:

wifi: ath11k: reset ar->num_stations on hardware start

When (multiple) hw restart occurs, we end up in a situation where we cannot accept new stations / mesh peers. This seems to be the 'num_stations' in 'struct ath11k' that did not get reset properly in this case. In ath11k_mac_op_start(), it was indeed the only accounting var that did not get reset so let's clear it too.

This avoids problems like those:

[1248828.088023] WARNING: CPU: 0 PID: 12281 at net/mac80211/util.c:1682 ieee80211_reconfig_stations+0x98/0xc0
[1248828.088115] Call trace:
[1248828.088116]  ieee80211_reconfig_stations+0x98/0xc0 (P)
[1248828.088119]  ieee80211_reconfig+0x774/0x1438
[1248828.088123]  ieee80211_restart_work+0x10c/0x178
[1248828.088127]  process_one_work+0x178/0x3c0
[1248828.088130]  worker_thread+0x280/0x440
[1248828.088133]  kthread+0xe0/0xf8
[1248828.088137]  ret_from_fork+0x10/0x20
[1248828.088141] ---[ end trace 0000000000000000 ]---
[1248836.686604] ath11k_pci 0000:04:00.0: refusing to associate station: too many connected already (128)
[1248836.686609] ath11k_pci 0000:04:00.0: Failed to add station: xx:xx:xx:xx:xx:xx for VDEV: 1

Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.9.0.1-01977-QCAHKSWPL_SILICONZ-1