Update rtnetlink requirement from 0.20.0 to 0.21.0 (#31)

Author: dependabot[bot]

Cargo.toml

@@ -26,7 +26,7 @@ tokio = { version = "1.48.0", features = ["rt"] }
 
 [target.'cfg(target_os = "linux")'.dependencies]
 nix = { version = "0.31.2", features = ["fs", "mount", "process"] }
-rtnetlink = "0.20.0"
+rtnetlink = "0.21.0"
 tempfile = "3.23.0"
 
 [target.'cfg(target_os = "macos")'.dependencies]