BINDTODEVICE for Direct Upstreams by #683

Co-Authored-By: brekotis <93345790+brekotis@users.noreply.github.com>

src/config/types.rs

@@ -1856,6 +1856,10 @@ pub enum UpstreamType {
         interface: Option<String>,
         #[serde(default)]
         bind_addresses: Option<Vec<String>>,
+        /// Linux-only hard interface pinning via `SO_BINDTODEVICE`.
+        /// Optional alias: `force_bind`.
+        #[serde(default, alias = "force_bind")]
+        bindtodevice: Option<String>,
     },
     Socks4 {
         address: String,