New version of jng (9.1)

[dteske]

Summary

Update examples and comments to return eifaces in exec.prestop
with ifconfig -vnet (before jng shutdown in poststop).

Reported by: jlduran
PR: 268397
MFC after: 1 week

[dteske]

Follow-up to D58903

[jlduran]

Thank you!
Arguably an improvement: in jail.xxx.conf, only keep xxx for the name itself and replace all other occurrences with s/xxx/${name}/.

[kfv]

Looks good to me. Thanks!