wifi: ath12k: fix A-MSDU indication in monitor mode

wifi: ath12k: fix A-MSDU indication in monitor mode

In monitor mode, host will reap MSDUs and then the MSDUs with same PPDU
ID will be aggregated into an A-MSDU in ath12k_dp_mon_rx_merg_msdus().

However, ath12k_dp_mon_rx_merg_msdus() doesn't calculate the total
length of the A-MSDU. This causes Wireshark to display the A-MSDU
incorrectly.

Therefore, need to add calculation of the A-MSDU length.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Kang Yang <quic_kangyang@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://patch.msgid.link/20241022110831.974-9-quic_kangyang@quicinc.com
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>