digsig: use ARRAY_SIZE() to compute array length

Use ARRAY_SIZE() to compute digsig_fs_blacklist length, rather than a
hardcoded length value.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: add cifs to list of network filesystems

Add cifs to list of network filesystems.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>