mptcp_expand_seq
new_snd_una = mptcp_expand_seq(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
mptcp_expand_seq(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
map_seq = mptcp_expand_seq(READ_ONCE(msk->ack_seq), mpext->data_seq, mpext->dsn64);