message: More reasonable read buffer size.
  Summary: A default of 4096 doesn't really make sense. The max MTU the internet is 1500, so pick that as a nice recognizable number, even though it is larger than we need.
diff: @@ -31,7 +31,7 @@ constexpr uint16_t kDefaultUDPSendPacketLen =
  : kDefaultV6UDPSendPacketLen);
  // This is the default if the transport parameter for max packet size is missing
  // or zero.
  -constexpr uint16_t kDefaultMaxUDPPayload = 65527;
  +constexpr uint16_t kDefaultMaxUDPPayload = 4096;
  // This is the minimum the max_packet_size transport parameter is allowed to be,
  // per the spec. Note this actually refers to the max UDP payload size, not the
  @@ -44,7 +44,7 @@ constexpr uint16_t kDefaultMsgSizeBackOffSize = 50;
  // Size of read buffer we provide to AsyncUDPSocket. The packet size cannot be
  // larger than this, unless configured otherwise.
  -constexpr uint16_t kDefaultUDPReadBufferSize = 4096;
  +constexpr uint16_t kDefaultUDPReadBufferSize = 1500;
  constexpr uint16_t kMaxNumCoalescedPackets = 5;
  // As per version 20 of the spec, transport parameters for private use must
  