Use pnet_datalink instead of all of pnet

pnet_transport takes a long time to build. It's been especially
painful from within a docker container for reasons I don't care
to understand. pnet_datalink is the only part of pnet we're using
so booting the rest.

src/bin/client-demo.rs

@@ -1,7 +1,6 @@
 extern crate atty;
 extern crate env_logger;
 extern crate getopts;
-extern crate pnet;
 extern crate rayon;
 extern crate serde_json;
 extern crate solana;

src/crdt.rs

@@ -17,7 +17,7 @@ use bincode::{deserialize, serialize};
 use byteorder::{LittleEndian, ReadBytesExt};
 use hash::Hash;
 use packet::{to_blob, Blob, BlobRecycler, SharedBlob, BLOB_SIZE};
-use pnet::datalink;
+use pnet_datalink as datalink;
 use rayon::prelude::*;
 use result::{Error, Result};
 use ring::rand::{SecureRandom, SystemRandom};

src/lib.rs

@@ -59,7 +59,7 @@ extern crate ring;
 extern crate serde;
 #[macro_use]
 extern crate serde_derive;
-extern crate pnet;
+extern crate pnet_datalink;
 extern crate serde_json;
 extern crate sha2;
 extern crate untrusted;