bittorrent-dht: only attempt to parse dht messages

The bittorrent flow is shared with transport messages as well as dht
messages. Only attempt to parse dht message as dht, ignore the rest.

rust/src/bittorrent_dht/bittorrent_dht.rs

@@ -92,7 +92,21 @@ impl BitTorrentDHTState {
         return tx;
     }
 
+    fn is_dht(input: &[u8]) -> bool {
+        if input.len() > 5 {
+            match &input[0..5] {
+                b"d1:ad" | b"d1:rd" | b"d2:ip" | b"d1:el" => true,
+                _ => false,
+            }
+        } else {
+            false
+        }
+    }
+
     pub fn parse(&mut self, input: &[u8]) -> bool {
+        if !Self::is_dht(input) {
+            return true;
+        }
         let mut tx = self.new_tx();
         let mut status = true;