add legacy connection toString (#604)

proxy/src/main/java/com/velocitypowered/proxy/connection/client/HandshakeSessionHandler.java

@@ -229,5 +229,10 @@ public class HandshakeSessionHandler implements MinecraftSessionHandler {
     public ProtocolVersion getProtocolVersion() {
       return ProtocolVersion.LEGACY;
     }
+
+    @Override
+    public String toString() {
+      return "[legacy connection] " + this.getRemoteAddress().toString();
+    }
   }
 }