route: Implement support for the ONLINK flag

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

Author: rwestphal

src/route/builder.rs

@@ -7,8 +7,8 @@ use std::{
 
 use netlink_packet_route::{
     route::{
-        RouteAddress, RouteAttribute, RouteHeader, RouteMessage, RouteProtocol,
-        RouteScope, RouteType,
+        RouteAddress, RouteAttribute, RouteFlags, RouteHeader, RouteMessage,
+        RouteProtocol, RouteScope, RouteType,
     },
     AddressFamily,
 };
@@ -96,6 +96,15 @@ impl<T> RouteMessageBuilder<T> {
         self
     }
 
+    /// Marks the next hop as directly reachable (on-link).
+    ///
+    /// Indicates that the next hop is reachable without passing through a
+    /// connected subnet.
+    pub fn onlink(mut self) -> Self {
+        self.message.header.flags.insert(RouteFlags::Onlink);
+        self
+    }
+
     /// Return a mutable reference to the request message.
     pub fn get_mut(&mut self) -> &mut RouteMessage {
         &mut self.message