restorer: introduced the struct krlimit

The layout of the struct rlimit depends on the value
of the macro FILE_OFFSET_BITS. If FILE_OFFSET_BITS is 64
the userspace and kernel definitions becomes incoherent
on a 32-bit platform.

The struct krlimit representing the kernel version of
the struct rlimit is introduced to address the issue:
the function restore_rlims() is fixed to convert between
the userspace and kernel representations of the struct.

Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>