SSH2_MSG_KEX_DH_GEX_REQUEST
if ((r = sshpkt_start(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST)) != 0 ||
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST,
ssh_dispatch_set(ssh, SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);