NFD

Implement hostname resolution routines to be shared between TcpChannel and UdpChannel.

1. The routine takes a FaceMgmt URI with scheme name { tcp, tcp4, tcp6, udp, udp4, udp6 }.
2. If the URI is valid, resolve hostname into IP addresses.
3. Pick one IP address. There's no requirement on round-robin. If scheme name is tcp4 or udp4, allow IPv4 only. If scheme name is tcp6 or udp6, allow IPv6 only. Otherwise, allow both IPv4 and IPv6.