Make hostname in next start match hostname the server is listening on

[Tenzer]

This is only a problem when using the default value for the hostname, as that
will make the server output > Ready on http://localhost:3000 to the console
while the server actually is listening on all IPv4 and IPv6 addresses, as
that's the default for the Node.js HTTP server when no hostname is provided.

[iamstarkov]

I don't understand why is this needed

[Tenzer]

It's in order to make the output of the next start command match what it's actually doing.

If I start a server with the default options, I get this output:

$ next start
> Ready on http://localhost:3000

So, based on that I would expect the server to be listening on localhost:3000, or 127.0.0.1:3000, but when I check with netstat it actually listens on all IP addresses, not just localhost:

$ netstat -an | grep .3000
tcp46      0      0  *.3000                 *.*                    LISTEN

If I however specify 'localhost' as the hostname to listen on, like this:

$ next start --hostname localhost
> Ready on http://localhost:3000

then the server correctly listens on the localhost IP address, 127.0.0.1:

$ netstat -an | grep .3000
tcp4       0      0  127.0.0.1.3000         *.*                    LISTEN

This PR changes the default listen address so it matches what the command outputs.

[timneutkens]

I don't think we should change the default as it can be breaking for a segment of users. The output is just a help for the user to easily open the running server.

[iamstarkov]

@timneutkens should it be closed then?

[timneutkens]

Yeah let's close this PR.

Thanks for taking the time to create a PR though 🙏 🙌