enum ofperr mf_check_src(const struct mf_subfield *, const struct flow *);
enum ofperr mf_check_dst(const struct mf_subfield *, const struct flow *);
enum ofperr mf_check_src(const struct mf_subfield *, const struct flow *);
enum ofperr mf_check_dst(const struct mf_subfield *, const struct flow *);