Correct data types related to delivery traffic indication map (DTIM)/
timing synchronization function (TSF) and implement/refine their
handling.  This information is used/needed by iwlwifi to set a station
as associated.  This will hopefully avoid more "no beacon heard"
time event failures.

The recording of the Linux specific sync_device_ts is done in the
receive path for now in case we do have the right information
available.  I need to investigate as to how-much it may make sense
to also migrate it into net80211 in the future depending on the
usage in other drivers (or how we did handle this in the past in
natively ported versions, e.g. iwm).

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days