ath10k: add accounting for the extended peer statistics

The 10.4 firmware adds extended peer information to the
firmware's statistics payload. This additional info is
stored as a separate data field and the elements are
stored in their own "peers_extd" list.

These elements can pile up in the same way as the peer
information elements. This is because the
ath10k_wmi_10_4_op_pull_fw_stats() function tries to
pull the same amount (num_peer_stats) for every statistic
data unit.

Fixes: 4a49ae94 ("ath10k: fix 10.4 extended peer stats update")
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>