wifi: ath12k: Fix NSS value update in ext_rx_stats

wifi: ath12k: Fix NSS value update in ext_rx_stats

Currently, in ext_rx_stats, the NSS value is taken directly from
the firmware, which results in incorrect mapping:
        4x4, 3x3, 2x2, 1x1 SS are incorrectly updated as 3x3, 2x2,
1x1, 0x0 SS respectively.

Fix the issue by incrementing the NSS value by 1 while updating
the PPDU info to ensure accurate spatial stream statistics.

Remove the redundant +1 increment in the radiotap header when monitor
mode is enabled to prevent double counting.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.5-01651-QCAHKSWPL_SILICONZ-1

Signed-off-by: Thiraviyam Mariyappan <thiraviyam.mariyappan@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20251007133332.1092178-1-thiraviyam.mariyappan@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>