initctl: resolve hierarchical cgroup limits

Cgroups v2 limits are hierarchical - a process is constrained by the
most restrictive limit in its ancestor chain, not just its immediate
cgroup.  This patch updates cg_conf() to walk up the hierarchy and
report effective limits by comparing values at each level.

This fixes incorrect "max" (unlimited) reporting in 'initctl --json
status', 'initctl cgroup', and 'initctl top' when child cgroups have
no explicit limits but parents do.

For memory.max and cpu.max: take minimum (most restrictive)
For memory.min: take maximum (most protection)

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/ChangeLog.md

@@ -33,6 +33,8 @@ All relevant changes are documented in this file.
   scroll wheel and Shift+PgUp/PgDn sometimes would not work properly
 - Fix flickering and artifacts in `initctl top`
 - Fix file descriptor leak in `initctl top`
+- Fix incorrect "max" limit reporting in `initctl [top|cgroup|--json]` output
+  for child cgroups.  Resolves effective limits by walking the cgroup hierarchy
 - Ensure mount/unmount skips `noauto` entries