For recent drivers we run into issues on TX in that we can
malloc/sleep. For the moment rather than replicating some logic
into drivers or compat framework start migrating a per-node mbufq
into net80211 and let the driver manage it. This allows the driver
to defer the TX for now avoiding locking issues.
Eventually the net80211/driver TX interface should improve and
most of the needed should be done in net80211.
I am just not there yet as to know what exactly we will end up with
so taking it one step at a time.
Also add a drv_data pointer where the driver can store state,
e.g., to backtrack its own internal view on the node.
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
X-MFC: wait longer, I just want the email