code: public final <T> UdpClient attr(AttributeKey<T> key, T value) {
  		Objects.requireNonNull(key, "key");
  		Objects.requireNonNull(value, "value");
  		return bootstrap(b -> b.attr(key, value));
  	}
docs: Inject default attribute to the future child {@link Channel} connections. They
  will be available via {@link Channel#attr(AttributeKey)}.
  
  @param key the attribute key
  @param value the attribute value
  @param <T> the attribute type
  
  @return a new {@link UdpClient}
  
  @see Bootstrap#attr(AttributeKey, Object)