cifs: check if SMB2 PDU size has been padded and suppress the warning

Some SMB2/3 servers, Win2016 but possibly others too, adds padding
not only between PDUs in a compound but also to the final PDU.
This padding extends the PDU to a multiple of 8 bytes.

Check if the unexpected length looks like this might be the case
and avoid triggering the log messages for :

  "SMB2 server sent bad RFC1001 len %d not %d\n"
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2misc.c

@@ -237,6 +237,13 @@ smb2_check_message(char *buf, unsigned int len, struct TCP_Server_Info *srvr)
 		if (clc_len == len + 1)
 			return 0;
 
+		/*
+		 * Some windows servers (win2016) will pad also the final
+		 * PDU in a compound to 8 bytes.
+		 */
+		if (((clc_len + 7) & ~7) == len)
+			return 0;
+
 		/*
 		 * MacOS server pads after SMB2.1 write response with 3 bytes
 		 * of junk. Other servers match RFC1001 len to actual