Select resolver automatically: `tart ip --resolver=auto`

[nirs]

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tart ip requires the user to select the right resolver, which makes the command harder to use. It can be easier it tart ip will pick the right resolver for the user based on the way the vm was run.

• If the vm was run with --net-softnet: use dhcpd
• If the vm was run with --net-bridged: use arp

The new mode can be named "auto"

If we don't have info on the way the vm was started tart ip can check all resolvers before it fails.