Add SO_REUSEADDR support

src/iface/interface/mod.rs

@@ -513,6 +513,7 @@ impl Interface {
         let mut processed_any = false;
 
         while let Some((rx_token, tx_token)) = device.receive(self.inner.now) {
+            rx_token.preprocess(sockets);
             let rx_meta = rx_token.meta();
             rx_token.consume(|frame| {
                 if frame.is_empty() {

src/iface/interface/udp.rs

@@ -25,12 +25,18 @@ impl InterfaceInner {
         ));
 
         #[cfg(feature = "socket-udp")]
-        for udp_socket in sockets
+        {
+            let mut is_received = false;
+            for udp_socket in sockets
             .items_mut()
             .filter_map(|i| UdpSocket::downcast_mut(&mut i.socket))
-        {
-            if udp_socket.accepts(self, &ip_repr, &udp_repr) {
-                udp_socket.process(self, meta, &ip_repr, &udp_repr, udp_packet.payload());
+                {
+                    if udp_socket.accepts(self, &ip_repr, &udp_repr) {
+                        udp_socket.process(self, meta, &ip_repr, &udp_repr, udp_packet.payload());
+                        is_received = true;
+                    }
+                }
+            if is_received {
                 return None;
             }
         }

src/phy/mod.rs

@@ -88,6 +88,7 @@ impl<'a> phy::TxToken for StmPhyTxToken<'a> {
 "##
 )]
 
+use crate::iface::SocketSet;
 use crate::time::Instant;
 
 #[cfg(all(
@@ -378,6 +379,11 @@ pub trait RxToken {
     fn meta(&self) -> PacketMeta {
         PacketMeta::default()
     }
+
+    /// Preprocess the incomming packet before it is passed to the stack.
+    ///
+    /// e.g., prepare TCP sockets when received a SYN packet.
+    fn preprocess(&self, _sockets: &mut SocketSet<'_>) {}
 }
 
 /// A token to transmit a single network packet.