TCPOLEN_MPTCP_MPC_SYN
len = TCPOLEN_MPTCP_MPC_SYN;
*size = TCPOLEN_MPTCP_MPC_SYN;
expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
if (opsize != TCPOLEN_MPTCP_MPC_SYN) {