Fix accidental removal of devfs_rulesets on jail stop

Pulls in a bugfix[0] that has been merged upstream[1].

This bug caused manually configured devfs_rulesets to get deleted on jail
stop, causing jails to come up with a default devfs rules on next start,
which can be a nuisance or even dangerous, depending on the specific setup.

Also adds a minimum devfs_ruleset id for dynamically created devfs rulesets
and fixes a devfs_ruleset resource leak when using plugins.

Take maintainership, as suggested by araujo@ (thanks for taking care of that
port for so long!).

[0]https://github.com/iocage/iocage/pull/1106
[1]https://github.com/iocage/iocage/commit/753b2f35731423597d7f51f33427b6d619fcd0b5

PR: 243510
Approved by: araujo (maintainer)
MFH: 2020Q1