LinuxKPI: 802.11: factor out dtim/tsf updates
Factor out dtim/tsf setting/updates into lkpi_update_dtim_tsf()
with tracing and add an extra update call.
This avoids some code duplication and puts maintainance into a
single place.
Sponsored by: The FreeBSD Foundation
(cherry picked from commit fa8f007de913623c066bf8f09213f92ee8cbca3a)