resolved: when DNS/TCP doesn't work, try DNS/UDP again

resolved: when DNS/TCP doesn't work, try DNS/UDP again

If we failed to contact a DNS server via TCP, bump of the feature level to UDP again. This way we'll switch back
between UDP and TCP if we fail to contact a host.

Generally, we prefer UDP over TCP, which is why UDP is a higher feature level. But some servers only support UDP but
not TCP hence when reaching the lowest feature level of TCP and want to downgrade from there, pick UDP again. We this
keep downgrading until we reach TCP and then we cycle through UDP and TCP.