task/cgroup/memory - ensure that ConstrainSwapSpace=no is correctly handled

Only set memory.memsw.limit_in_bytes to the computed amount of allowed
RAM+Swap when ConstrainSwapSpace=yes in cgroup.conf.
When ConstrainSwapSpace=yes and ConstrainRAMSpace=no, automatically
set AllowedRAMSpace to 100% in order to compute the memsw.limit based
on the allocated memory plus the allowed swap percent. Then use that
limit for both mem and mem+sw limits.