conf.c: Cast st_uid and st_gid to int

In eglibc st_uid and st_gid are defined as unsigned integers, in bionic those
are defined as unsigned long (which is inconsistent with the kernel's
defintion that's uint_32).

To workaround this problem, simply cast those two to int.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>