ath10k: support use of channel 173

The India regulatory domain allows CH 173, so add that to the
available channel list.  I verified basic connectivity between
a 9880 and 9984 NIC.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>