wifi: ath12k: export ath12k_wmi_tlv_hdr for testmode

Export ath12k_wmi_tlv_hdr() to further use in the testmode command
processing.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00173-QCAHKSWPL_SILICONZ-1

Signed-off-by: Aaradhana Sahu <quic_aarasahu@quicinc.com>
Reviewed-by: Aditya Kumar Singh <quic_adisi@quicinc.com>
Link: https://patch.msgid.link/20250119083657.1937557-3-quic_aarasahu@quicinc.com


Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>