mac80211: allow setting queue_len for drivers not using wake_tx_queue

Currently a mac80211 driver can only set the txq_limit when using
wake_tx_queue. Not all drivers use wake_tx_queue. This patch adds a new
element to wiphy allowing a driver to set a custom tx_queue_len and the
code that will apply it in case it is set. The current default is
1000 which is too low for ath11k when doing HE rates.

Signed-off-by: John Crispin <john@phrozen.org>
Link: https://lore.kernel.org/r/20200211122605.13002-1-john@phrozen.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>