cgroup: Respect DefaultMemoryMin when setting memory.min

cgroup: Respect DefaultMemoryMin when setting memory.min

This is an oversight from https://github.com/systemd/systemd/pull/12332.

Sadly the tests didn't catch it since it requires a real cgroup
hierarchy to see, and it wasn't seen in prod since we're only currently
using DefaultMemoryLow, not DefaultMemoryMin. :-(

(cherry picked from commit 64fe532e90b3e99bf7821ded8a1107c239099e40)
(cherry picked from commit f14e3e02cca759dc92c87328e257acc6abe91cbc)

Gbp-Pq: Name cgroup-Respect-DefaultMemoryMin-when-setting-memory.min.patch