Improve ignore network interface implementation

Several improvements for the ignore network interfaces implementation

• build option ignored-network-interface-prefix now accepts a comma-separated list of strings
  • libnice can now be configured to ignore more than one prefix
  • the default list is docker, veth, virbr and vnet
• ignore interfaces that are not running
• also mark a IPv6 private (ULA) or link-local address as a private IP address
• sync the implementations for HAVE_GETIFADDRS and !HAVE_GETIFADDRS

Fixes #87 (closed)