ath10k: implement more versatile set_bitrate_mask

Until now only a single fixed tx rate or nss was
allowed to be set.

The patch attempts to improve this by allowing
most bitrate masks. The limitation is VHT MCS
rates cannot be expressed separately using
existing firmware interfaces and only the
following VHT MCS ranges are supported: none, 0-7,
0-8, and 0-9.

This keeps the old behaviour when requesting
single tx rate or single nss. The new bitrate mask
logic is only applied to other cases that would
return -EINVAL until now.

Depending on firmware revisions some combinations
may crash firmware so use with care, please.

This depends on "ath10k: don't use reassoc flag".
Without it key cache would effectively be
invalidated upon bitrate change leading to
communication being no longer possible.

These work:

  iw wlan0 set bitrates legacy-5 6 12 ht-mcs-5 1 2 3
  iw wlan0 set bitrates legacy-5 ht-mcs-5 7 8 9
  iw wlan0 set bitrates legacy-5 24 ht-mcs-5 vht-mcs-5 1:0-9

These won't work:

  iw wlan0 set bitrates legacy-5 ht-mcs-5 vht-mcs-5 1:0-5
  iw wlan0 set bitrates vht-mcs-5 2:7-9

(note the invalid VHT MCS ranges)

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>