Feature request: Better IPv6 support.

[haight6716]

Describe the bug
Using dynamic-public-ip on a host with an IPv6 interface, only the v6 IP is advertised and this leads to the node being marked not accessible.

To Reproduce

• Start a node using dynamic-public-ip: opendns on a host with a v6 IP address and v4 IP address.
• getNodeIP

Expected behavior
v4 IP address is reported, or better, multiple IPs are reported.

Screenshots

# curl -X POST --data '{
    "jsonrpc":"2.0",
    "id"     :1,
    "method" :"info.getNodeIP"
}' -H 'content-type:application/json;' 127.0.0.1:9650/ext/info
{"jsonrpc":"2.0","result":{"ip":"[2601:602:8e00:2e7d:92a5:3172:1eba:daf]:9651"},"id":1}

Operating System
PoPOS (Ubuntu) 21.10

Additional context
Workaround: if dynamic-public-ip: ifconfigme is used, a v4 IP is returned & advertised.

IMO Ideally we could publish multiple IPs, either v4 or v6 and the client could decide which to use, preferring v6, but falling back to v4. v4 and v6 IPs would be detected by dyndns and advertised automatically when in dynamic-public-ip mode.

Alternately, we could stop penalizing hosts only advertising v6 IPs.

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[StephenButtolph]

As far as I can tell, avalanchego fully supports IPv6. The only issues I've ever run into with avalanchego and IPv6 have been because inbound traffic on the IPv6 address was not being allowed (which we attempt to handle as a best effort support with the NAT traversal... but isn't really guaranteed by avalanchego). I'm going to close this because I don't think there is actually a bug in avalanchego here... but if there is something to replicate where the IPv6 address is reachable and avalanchego is reporting that IP and is not servicing requests then feel free to re-open this.