message: Change the safe SCTP MTU size to 1191
  Cr-Commit-Position: refs/heads/master@{#33338}
diff: @@ -55,8 +55,19 @@ constexpr int kSctpSuccessReturn = 1;
  namespace {
  // The biggest SCTP packet. Starting from a 'safe' wire MTU value of 1280,
  -// take off 80 bytes for DTLS/TURN/TCP/IP overhead.
  -static constexpr size_t kSctpMtu = 1200;
  +// take off 85 bytes for DTLS/TURN/TCP/IP and ciphertext overhead.
  +//
  +// Additionally, it's possible that TURN adds an additional 4 bytes of overhead
  +// after a channel has been established, so we subtract an additional 4 bytes.
  +//
  +// 1280 IPV6 MTU
  +// -40 IPV6 header
  +// -8 UDP
  +// -24 GCM Cipher
  +// -13 DTLS record header
  +// -4 TURN ChannelData
  +// = 1191 bytes.
  +static constexpr size_t kSctpMtu = 1191;
  // Set the initial value of the static SCTP Data Engines reference count.
  ABSL_CONST_INIT int g_usrsctp_usage_count = 0;
  