SMB3.1.1: fix mount failure to some servers when compression enabled

When sending the compression context to some servers, they rejected
the SMB3.1.1 negotiate protocol because they expect the compression
context to have a data length of a multiple of 8.
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2pdu.h

@@ -394,6 +394,7 @@ struct smb2_compression_capabilities_context {
 	__u16	Padding;
 	__u32	Flags;
 	__le16	CompressionAlgorithms[3];
+	__u16	Pad;  /* Some servers require pad to DataLen multiple of 8 */
 	/* Check if pad needed */
 } __packed;