LinuxKPI: 802.11: no need to lock during lkpi_lsta_alloc()

Given upon sta allocation we do not adjust the chanctx in case of
mismatch there is not need to lock here.
This fixes a problem that upon shutdown net80211 once again can
race into here replacing the node from a context where it is holding
a lock which does not allow us to hold an sx lock (sleeping thread
holds a non-sleepable lock).

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reported by: ziaee
Tested by: ziaee