iwlwifi: add FreeBSD specific debugging

"Invalid TXQ id" and "Queue <n> is stuck <x> <y>" are two errors seen
more commonly by FreeBSD users. Try to gather some extra data the
"easy way" adding more error logging for these situations in the hope
to find a clue or at least do more targetd debugging in the future.
Note that for one of the errors the Linux Intel driver has a TODO to
print register data. If that will show up in future versions of the
driver this may also help.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days