patch 46/47 causes NULL pointer deref on mt7921

[Bert Karwatzki]

I looked more close at the call trace of the warning and it seems that the
problems 
occur when shutting down the interface:
[  T847] Call Trace:
[  T847]  <TASK>
[  T847]  ? __warn+0x6a/0xc0
[  T847]  ? mt7921_ipv6_addr_change+0x1d0/0x1f0 [mt7921_common]
[  T847]  ? report_bug+0x142/0x180
[  T847]  ? handle_bug+0x3a/0x70
[  T847]  ? exc_invalid_op+0x17/0x70
[  T847]  ? asm_exc_invalid_op+0x1a/0x20
[  T847]  ? mt7921_ipv6_addr_change+0x1d0/0x1f0 [mt7921_common]
[  T847]  ? srso_alias_return_thunk+0x5/0xfbef5
[  T847]  ? __ipv6_ifa_notify+0x16f/0x4d0
[  T847]  ? ieee80211_ifa6_changed+0x5e/0x70 [mac80211]
[  T847]  ? atomic_notifier_call_chain+0x51/0x80
[  T847]  ? addrconf_ifdown.isra.0+0x43f/0x810
[  T847]  ? srso_alias_return_thunk+0x5/0xfbef5
[  T847]  ? addrconf_notify+0x15d/0x760
[  T847]  ? __timer_delete_sync+0x70/0xd0
[  T847]  ? raw_notifier_call_chain+0x43/0x60
[  T847]  ? dev_close_many+0xea/0x160
[  T847]  ? dev_close+0x65/0x80
[  T847]  ? cfg80211_shutdown_all_interfaces+0x48/0xe0 [cfg80211]
[  T847]  ? cfg80211_rfkill_set_block+0x25/0x40 [cfg80211]
[  T847]  ? rfkill_set_block+0x8f/0x160 [rfkill]
[  T847]  ? rfkill_fop_write+0x14e/0x1e0 [rfkill]
[  T847]  ? vfs_write+0xf3/0x420
[  T847]  ? srso_alias_return_thunk+0x5/0xfbef5
[  T847]  ? ksys_write+0xae/0xe0
[  T847]  ? do_syscall_64+0x5f/0x170
[  T847]  ? entry_SYSCALL_64_after_hwframe+0x55/0x5d
[  T847]  </TASK>
[  T847] ---[ end trace 0000000000000000 ]---

I think there's a race happening on shutdown between ipv6_addr_change (which
uses mvif->phy)
and ieee80211_do_stop (which zeros the private data including mvif->phy).

Resend with fixed formatting.

Bert Karwatzki