LinuxKPI: 802.11: improve lkpi_ic_vap_delete()

Changing the order of cleanup in lkpi_ic_vap_delete() will avoid
firmware crashes or a direct panic as observed as ieee80211_vap_detach()
will do most cleanup for us and get us into the correct state.

The solution is not fully developed yet and one may not be able
to create a new vap (lkpi_ic_vap_create may fail with error 17)
afterwards. It is supposed to be a step towards more stability
for now.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
PR: 269842