staging: wfx: simplify the link-id allocation

staging: wfx: simplify the link-id allocation

The "link-id" is a slot number provided to the chip. A link-id is
allocated to every station associated with the chip (mainly when the
chip is in AP mode). It is more or less the same thing than the
association ID, but it is limited to 14 values.

Firmware uses the link-id to track the power save status of the
stations.

The current code try to associate a link-id as soon as data are
exchanged with station. It is far easier to rely on sta_add() and
sta_remove().

Until now the value WFX_LINK_ID_NO_ASSOC, was only used when no more
link-id was available. Now, we also use this value for
not-yet-associated stations (that was its primary behavior).

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200115135338.14374-51-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>