consistently use smb_buf_length as be32 for cifs (try 3)

There is one big endian field in the cifs protocol, the RFC1001
       length, which cifs code (unlike in the smb2 code) had been handling as
       u32 until the last possible moment, when it was converted to be32 (its
       native form) before sending on the wire.   To remove the last sparse
       endian warning, and to make this consistent with the smb2
       implementation  (which always treats the fields in their
       native size and endianness), convert all uses of smb_buf_length to
       be32.

       This version incorporates Christoph's comment about
       using be32_add_cpu, and fixes a typo in the second
       version of the patch.

Signed-off-by: Steve French <sfrench@us.ibm.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/cifspdu.h

@@ -397,9 +397,9 @@
 #define GETU32(var)  (*((__u32 *)var))	/* BB check for endian issues */
 
 struct smb_hdr {
-	__u32 smb_buf_length;	/* big endian on wire *//* BB length is only two
-		or three bytes - with one or two byte type preceding it that are
-		zero - we could mask the type byte off just in case BB */
+	__be32 smb_buf_length;	/* BB length is only two (rarely three) bytes,
+		with one or two byte "type" preceding it that will be
+		zero - we could mask the type byte off */
 	__u8 Protocol[4];
 	__u8 Command;
 	union {