Allow inherit/ip_hostname as IP options

[tschettervictor]

#788
#369
#702
#535
#521

Testing

create jail with the below options

inherit as the IP
ip_hostname as the IP
Then do both the above with the "-D|--dual" switch and you should find that it will set them for "ip4" and "ip6"
If you do not ise the -D option, IP6 will be disabled and only ip4 will be set.

Ensure that jails start and stop properly with all the above combinations.

Note: You might need PR #765 if you use RDR at all.

[bmac2]

tested on my server with ipv4. Works as advertised. I don't have ipv6 on my network so did not test that.

@yaazkal AFTER 765 this one is ready to test

@tschettervictor