Set IP(V6)_RECVERR on connect UDP sockets (via libuv)

The connect()ed UDP socket provides feedback on a variety of ICMP errors (eg port unreachable) which bind can then use to decide what to do with errors (report them to the client, try again with a different nameserver etc). However, Linux's implementation does not report what it considers "transient" conditions, which is defined as Destination host Unreachable, Destination network unreachable, Source Route Failed and Message Too Big.

Explicitly enable IP_RECVERR / IPV6_RECVERR (via libuv uv_udp_bind() flag) to learn about ICMP destination network/host unreachable.

Closes #835 (closed)