docs: recommend disabling ipv6

[thephez]

Related to dashpay/platform#2100 and https://www.dash.org/forum/index.php?threads/dashmate-incorrectly-shows-ports-as-closed.55244/

Preview build: https://dash-docs--390.org.readthedocs.build/en/390/docs/user/masternodes/server-config.html#set-up-your-vps

[thephez]

@kxcd what do you think about this?

[thephez]

Updated per discord feedback

[pshenmic]

Recommending switching off the whole IPV6 stack because one of the external service providers is not accepting it looks weird for me, as it does not even actually bother any core / platform software. Alongside with continued IPV4 address pool extinction I think its more valuable to encourage increasing support IPV6 rather than just simply dropping it.

In our case I guess dashmate can do an explicit DNS lookup before calling MNOWatch's API via IP Address instead of DNS name (because nodejs now prefer ipv6 over ipv4 when querying DNS).

I think it would be really great to see MNOWatch start supporting IPV6, @kxcd if that's possible it would be the best

As another solution from the dashmate side, I guess we can switch from MNOWatch to simply telnet-ing specific ports on a node's external IP.