the tlv len is set to the total len of the wmi cmd, it will trigger
firmware crash, correct the tlv len.

Tested with QCA6174 SDIO with firmware
WLAN.RMH.4.4.1-00017-QCARMSWP-1 and QCA6174
PCIE with firmware WLAN.RM.4.4.1-00110-QCARMSWPZ-1.

Fixes: ce834e28 ("ath10k: support NET_DETECT WoWLAN feature")
Signed-off-by: Wen Gong <wgong@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>