nzrdhcp: also define lease in offer

nzrdhcp/src/main.rs

@@ -78,12 +78,15 @@ async fn handle_message(ctx: &Context, from: SocketAddr, msg: &Message) {
     let mut nak = false;
 
     let mut response = match msg_type {
-        MessageType::Discover => make_reply(
-            msg,
-            MessageType::Offer,
-            Some(instance.lease.addr.addr),
-            true,
-        ),
+        MessageType::Discover => {
+            lease_time = Some(DEFAULT_LEASE);
+            make_reply(
+                msg,
+                MessageType::Offer,
+                Some(instance.lease.addr.addr),
+                true,
+            )
+        }
         MessageType::Request => {
             if let Some(DhcpOption::RequestedIpAddress(addr)) =
                 msg.opts().get(OptionCode::RequestedIpAddress)