Resolves renaming netgraph jails. Previous behavior would "replace" the jng commands with the same old interface then fail to start the newly renamed jail with the following output.
```sh
Attempting to rename 'testjail' to jt...
Renamed 'testjail' to 'jt' successfully.
[jt]:
ng0_testjail
jt: created
ifconfig: interface ng0_jt does not exist
jail: jt: /sbin/ifconfig ng0_jt vnet jt: failed
jt: removed
```
The failure case above required manually creating the netgraph interface with `jng bridge <new ng int suffix> <interface>` and removing the old one `jng shutdown <old ng int suffix>`
f98a2925cc