add support for setting up routing inside the netns

src/up.rs

@@ -1,4 +1,5 @@
 use crate::config::{Config, NamespaceName};
+use crate::link::{LinkError, LinkManager};
 use crate::namespace::NetNs;
 use main_error::MainResult;
 use tracing::error;
@@ -24,6 +25,14 @@ pub fn up(config: Config) -> MainResult {
                 error!(%error, "failed to move device into namespace");
             }
         }
+        for route in new.routes {
+            namespace.handle().run_in(|| {
+                let manager = LinkManager::new()?;
+                let link = manager.get_link(&route.device)?;
+                manager.add_route(&link, route.destination)?;
+                Ok::<_, LinkError>(())
+            })??;
+        }
     }
 
     Ok(())