LinuxKPI: 802.11: Always lock around lkpi_{ic_vap_delete,mo_stop}()

[temcbun_gmail.com]

Summary

Add the missing locking as drivers always expect it (by assertion) and
cannot distinguish between state.

Add the assertions to the downcalls as we need both of them locked
and both of them can sleep.

PR: 298417

I tried to implement the changes to fix the bug, introduced in the PR, based on 5d479b75a894, which fixed the similar problem.

Test Plan

With this patch applied and the INVARIANTS kernel, destroying the rtw89(4) interface should not freeze the system:

$ ifconfig wlan create wlandev rtw890
wlan0
$ ifconfig wlan0 destroy