Correct cfg attributes

Cargo.toml

@@ -45,6 +45,8 @@ tokio-util = "0.7.11"
 nftables = { git = "https://github.com/hack3ric/rust-nftables", branch = "for-flow", features = [
   "tokio",
 ] }
+
+[target.'cfg(any(target_os = "linux", target_os = "freebsd"))'.dependencies]
 rtnetlink = { git = "https://github.com/hack3ric/rust-rtnetlink", branch = "for-flow" }
 
 [dev-dependencies]

src/kernel/mod.rs

@@ -34,6 +34,7 @@ pub trait Kernel: Sized {
     pending()
   }
 
+  /// Drops the kernel interface and do asynchronous cleanups.
   fn terminate(self) -> impl Future<Output = ()> {
     ready(())
   }
@@ -63,13 +64,15 @@ impl Kernel for KernelAdapter {
   async fn apply(&mut self, spec: &Flowspec, info: &RouteInfo<'_>) -> Result<Self::Handle> {
     match self {
       Self::Noop => Ok(KernelHandle::Noop),
+      #[cfg(target_os = "linux")]
       Self::Linux(linux) => Ok(KernelHandle::Linux(linux.apply(spec, info).await?)),
     }
   }
 
   async fn remove(&mut self, handle: Self::Handle) -> Result<()> {
     match (self, handle) {
       (Self::Noop, KernelHandle::Noop) => Ok(()),
+      #[cfg(target_os = "linux")]
       (Self::Linux(linux), KernelHandle::Linux(handle)) => linux.remove(handle).await,
       _ => Err(Error::HandleMismatch),
     }
@@ -78,13 +81,15 @@ impl Kernel for KernelAdapter {
   async fn process(&mut self) -> Result<()> {
     match self {
       Self::Noop => pending().await,
+      #[cfg(target_os = "linux")]
       Self::Linux(linux) => linux.process().await,
     }
   }
 
   async fn terminate(self) {
     match self {
       Self::Noop => {}
+      #[cfg(target_os = "linux")]
       Self::Linux(linux) => linux.terminate().await,
     }
   }