iwlwifi: mvm: fix AC / FIFO mapping

The AC / fifo mapping was wrong - BE packets landed in VO
FIFO. The iwl_mvm_tx_fifo enumeration isn't in the same
order as ieee80211_ac_numbers enumeration.
Since the firmware relies on fifo / ac mapping - this led
to wrong behavior. E.g. the firmware sends beacon with the
same QoS parameters as VO, and it actually took the
parameters of BK. There are probably more severe issues.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>