Use rlim_t where appropriate

I got the following then trying to compile CRIU on ARM with clang:

> criu/cr-restore.c:2476:22: error: implicit conversion from 'unsigned
> long long' to 'unsigned long' changes value from 18446744073709551615 to
> 4294967295 [-Werror,-Wconstant-conversion]
>         return ival == -1 ? RLIM_INFINITY : ival;
>         ~~~~~~              ^~~~~~~~~~~~~
> /usr/include/arm-linux-gnueabihf/bits/resource.h:117:24: note: expanded
> from macro 'RLIM_INFINITY'
> # define RLIM_INFINITY 0xffffffffffffffffuLL
>                        ^~~~~~~~~~~~~~~~~~~~~
> 1 error generated.

Fix by using provided rlim_t type in this and similar places.

travis-ci: success for Fixes to compile on arm with clang
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>