mwifiex: correct TX byte count statistics

The skb is modified in sending the TX packet. Save the original
packet length to a variable so that we can get the correct
statistics update.

Signed-off-by: Ujjal Roy <royujjal@gmail.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/mwifiex/decl.h b/drivers/net/wireless/mwifiex/decl.h
index 5c85d78..3a21bd0 100644
--- a/drivers/net/wireless/mwifiex/decl.h
+++ b/drivers/net/wireless/mwifiex/decl.h
@@ -130,6 +130,7 @@
 	u8 flags;
 	u8 bss_num;
 	u8 bss_type;
+	u32 pkt_len;
 };
 
 enum mwifiex_wmm_ac_e {