Class linger

src/socket.cpp:950–950

#ifdef USE_SCTP
        if (ss_transport == T_SCTP && !gracefulclose) {
            struct linger ling = {1, 0};
            if (setsockopt(ss_fd, SOL_SOCKET, SO_LINGER, &ling, sizeof(ling)) < 0) {
                WARNING("Unable to set SO_LINGER option for SCTP close");
            }