Fix several issues introduced with iwm(4) Tx aggregation support.

Fix several issues introduced with iwm(4) Tx aggregation support.

Keep station queues marked as enabled until the device gets reset.
The firmware becomes unhappy if it finds some queues enabled but missing
from the station's queue mask, even across removals and re-additions of the
station which occur during re-associations and while roaming between APs.
Fixes "could not add sta (error 35)" fatal firmware errors.

When stopping a BA session, properly set the bit corresponding to the
session's TID in the node's tid_disable_ampu bitmask.

During dis- and re-associations all Tx block ack sessions are torn down,
so clear the bitmask which identifies queues with active Tx BA sessions.

Don't byte-swap values written to host-side variables.

Problems reported and fixes tested by Matthias Schmidt and kettenis@.
Additional testing by phessler@, mlarkin@, and Mikolaj Kucharski.