update dhcp example to work in the case where we do not already have an ip address from some other source

Author: jlogan03

examples/dhcp_client.rs

@@ -38,6 +38,15 @@ fn main() {
     config.random_seed = rand::random();
     let mut iface = Interface::new(config, &mut device, Instant::now());
 
+    // Initialize with an address so that there is something to mutate later.
+    // This also allows sockets made before a real address is negotiated
+    // via DHCP to update properly afterward.
+    iface.update_ip_addrs(|addrs| {
+        addrs
+            .push(IpCidr::Ipv4(Ipv4Cidr::new(Ipv4Address::UNSPECIFIED, 0)))
+            .unwrap();
+    });
+
     // Create sockets
     let mut dhcp_socket = dhcpv4::Socket::new();
 
@@ -86,6 +95,7 @@ fn main() {
     }
 }
 
+/// Mutate the first IP address to match the one supplied
 fn set_ipv4_addr(iface: &mut Interface, cidr: Ipv4Cidr) {
     iface.update_ip_addrs(|addrs| {
         let dest = addrs.iter_mut().next().unwrap();