Add example for list interfaces

examples/interfaces.rs

@@ -0,0 +1,22 @@
+extern crate nix;
+
+
+#[allow(dead_code)]
+fn pretty_print(ifaddr: &nix::ifaddrs::InterfaceAddress) {
+    println!("{}: flags={:X}<{}>", 
+        ifaddr.interface_name, 
+        ifaddr.flags.bits(),
+        format!("{:?}", ifaddr.flags).replace("IFF_", "").replace(" | ", ","));
+    println!("    address    : {}", ifaddr.address.map(|a| format!("{}", a)).unwrap_or("N/A".to_string()));
+    println!("    netmask    : {}", ifaddr.netmask.map(|a| format!("{}", a)).unwrap_or("N/A".to_string()));
+    println!("    broadcast  : {}", ifaddr.broadcast.map(|a| format!("{}", a)).unwrap_or("N/A".to_string()));
+    println!("    destination: {}", ifaddr.destination.map(|a| format!("{}", a)).unwrap_or("N/A".to_string()));
+}
+
+fn main (){
+    let addrs = nix::ifaddrs::getifaddrs().unwrap();
+    for ifaddr in addrs {
+        println!("{:?}", ifaddr);
+        // pretty_print(&ifaddr);
+    }
+}