mac80211: fix parameter reading for AC_BE tx bursting

mac80211: fix parameter reading for AC_BE tx bursting

The "tx_burst" option which should control the value was
expecting more of a list and hence tx_queue_data2_burst
value wasn't updated.

Yes, it would make sense to have a list for this, the
existing  code only updates tx_queue_data2_burst and
not the other tx_queue_data[0134]_burst values.

Signed-off-by: Alberto Martinez-Alvarez <amteza@gmail.com>
(formatted commit message, wrote extra information into commit,
moved tx_burst to existing json_get_vars)
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>