s4:dsdb/schema: add dsdb_syntax_INT32_validate_ldb()

[tridge at samba.org]

Hi Metze,

Thanks for all of the great work you've been doing on ldb validation!

Some comments on ece3defd15246f232acaf0c2c29b66da2924438a

You use:

  char buf[sizeof("-2147483648")];

and this test:

	if (in->values[i].length >= sizeof(buf)) {
		return WERR_DS_INVALID_ATTRIBUTE_SYNTAX;
	}

That will fail if someone passes in a an integer of maximum size with
a nul termination byte. I think you should either add a +1 to the
sizeof(), or you could specifically check for nul termination (eg. use
strnlen(in->values[i].data, in->values[i].length) as the length to
test against).

Cheers, Tridge