Ping using specific interface: support IPv6?

[chucker]

Obviously, we should, right?

There are a few issues with that, like: how do we know which address is preferred? What if IPv6 doesn't work but IPv4 would've? Do we add another picker? (Ew.)

Having one picker but actually showing addresses grouped by interface might be an option. But XamForms doesn't seem to support groups/sections?