nrf_wifi: Fix missing L2 header in max MSDU calculation

MTU doesn't include any L2 overhead, so, we need to add Ethernet header
len for maximum frame size that we can received from the networking
stack.

Fixes SHEL-2214.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

nrf_wifi/fw_if/umac_if/src/default/fmac_api.c

@@ -532,7 +532,8 @@ struct nrf_wifi_fmac_priv *nrf_wifi_fmac_init(struct nrf_wifi_data_config_params
 			def_priv->rx_buf_pools[pool_idx].buf_sz + RX_BUF_HEADROOM;
 	}
 
-	hal_cfg_params.max_tx_frm_sz = CONFIG_NRF_WIFI_IFACE_MTU + TX_BUF_HEADROOM;
+	hal_cfg_params.max_tx_frm_sz = CONFIG_NRF_WIFI_IFACE_MTU + NRF_WIFI_FMAC_ETH_HDR_LEN +
+					TX_BUF_HEADROOM;
 
 	hal_cfg_params.max_cmd_size = MAX_NRF_WIFI_UMAC_CMD_SIZE;
 	hal_cfg_params.max_event_size = MAX_EVENT_POOL_LEN;