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

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