ath11k: fix netdev open race

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

ath11k: fix netdev open race

Make sure to allocate resources needed before registering the device.

This specifically avoids having a racing open() trigger a BUG_ON() in
mod_timer() when ath11k_mac_op_start() is called before the
mon_reap_timer as been set up.

I did not see this issue with next-20220310, but I hit it on every probe
with next-20220511. Perhaps some timing changed in between.

Here's the backtrace:

[ 51.346947] kernel BUG at kernel/time/timer.c:990!
[ 51.346958] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
...
[ 51.578225] Call trace:
[ 51.583293] __mod_timer+0x298/0x390
[ 51.589518] mod_timer+0x14/0x20
[ 51.595368] ath11k_mac_op_start+0x41c/0x4a0 [ath11k]
[ 51.603165] drv_start+0x38/0x60 [mac80211]
[ 51.610110] ieee80211_do_open+0x29c/0x7d0 [mac80211]
[ 51.617945] ieee80211_open+0x60/0xb0 [mac80211]
[ 51.625311] __dev_open+0x100/0x1c0
[ 51.631420] __dev_change_flags+0x194/0x210
[ 51.638214] dev_change_flags+0x24/0x70
[ 51.644646] do_setlink+0x228/0xdb0
[ 51.650723] __rtnl_newlink+0x460/0x830
[ 51.657162] rtnl_newlink+0x4c/0x80
[ 51.663229] rtnetlink_rcv_msg+0x124/0x390
[ 51.669917] netlink_rcv_skb+0x58/0x130
[ 51.676314] rtnetlink_rcv+0x18/0x30
[ 51.682460] netlink_unicast+0x250/0x310
[ 51.688960] netlink_sendmsg+0x19c/0x3e0
[ 51.695458] ____sys_sendmsg+0x220/0x290
[ 51.701938] ___sys_sendmsg+0x7c/0xc0
[ 51.708148] __sys_sendmsg+0x68/0xd0
[ 51.714254] __arm64_sys_sendmsg+0x28/0x40
[ 51.720900] invoke_syscall+0x48/0x120

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3