cifs: mask off top byte in get_rfc1002_length()

The rfc1002 length actually includes a type byte, which we aren't
masking off. In most cases, it's not a problem since the
RFC1002_SESSION_MESSAGE type is 0, but when doing a RFC1002 session
establishment, the type is non-zero and that throws off the returned
length.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsglob.h

@@ -513,7 +513,7 @@ struct cifs_mnt_data {
 static inline unsigned int
 get_rfc1002_length(void *buf)
 {
-	return be32_to_cpu(*((__be32 *)buf));
+	return be32_to_cpu(*((__be32 *)buf)) & 0xffffff;
 }
 
 static inline void