Fix deprecation warning on ping and dns binaries
Created by: Nickforall
I noticed some deprecation warnings in netutils when updating my build today, and thought it was a good first rusty contribution to Redox.
Since rust-lang/rust#47510, lookup_host host is deprecated, and the way to resolve IP addresses is now using std::net::ToSocketAddrs.
Again, this is my first Rust contribution to Redox, so please let me know if something is wrong, you can also reach me on the chat.