Allow for VLAN name to be used for IP address allocation in host add.

[terjekv]

For both maintenance of IP ranges and ease of use, being able to do host add -ip my-network -mac xx:xx:xx:xx:xx myboks.dns would be really nice.

[oyvindkolbu]

Possible better with a -vlan name or -vlanid 1234? What about vlan with both ipv4 and ipv6? Assign both? Vlan with multiple ipv4/ipv6-networks could just give an error and ask to be more explicit?

The actual coding is pretty trivial.

[terjekv]

If the VLAN IDs are duplicated between networks for both IPv4 and IPv6, one possible set of semantics are:

-vlanid 200, -vlanid 200:ipv4, and -vlanid 200:ipv6. The first one returns both addresses. -vlan name is certainly also cleaner than reusing -ip.