ath10k: add per peer htt tx stats support for 10.4

Per peer tx stats are part of 'HTT_10_4_T2H_MSG_TYPE_PEER_STATS'
event, Firmware sends one HTT event for every four PPDUs.
HTT payload has success pkts/bytes, failed pkts/bytes, retry
pkts/bytes and rate info per ppdu.
Peer stats are enabled through 'WMI_SERVICE_PEER_STATS',
which are nowadays enabled by default.

Parse peer stats and update the tx rate information per STA.

tx rate, Peer stats are tested on QCA4019 with Firmware version
10.4-3.2.1-00028.

Signed-off-by: Anilkumar Kolli <akolli@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>