s4:dsdb/schema: add dsdb_syntax_INT32_validate_ldb()

[tridge at samba.org]

Hi Metze,

 > Does Windows allow an extra \0 byte?

I just tested and it doesn't allow the \0 byte. Interestingly, it also
doesn't allow the \0 byte even for small integer values, so I guess we
should make dsdb_syntax_INT32_validate_ldb() even stricter, and check
that strnlen(v->data, v->length) == v->length.

 > My aim was to make us as strict as possible first and then
 > demonstrate with tests that we need to be less strict.

and I think this demonstrates that you're taking the right approach :-)

Cheers, Tridge