No IPv4 fallback when IPv6 is not working

[laeti-tia]

When pSConfig tries to reach a remote JSON mesh file over IPv6 and this is not reachable for some reasons, it seems it doesn't try to fall back to IPv4 transport. That's usually what the tools do when used on a dual-stack machine, for example curl can fetch the remote JSON file using IPv4, after timing out trying to use IPv6.

Not a high priority, but probably good to solve together with perfsonar/project#1273