sadb_prop
struct sadb_prop *prop = (void *)ext;
sizeof(struct sadb_prop), /* SADB_EXT_PROPOSAL */
struct sadb_prop *prop;
const int l = PFKEY_ALIGN8(sizeof(struct sadb_prop));
prop = mtod(m, struct sadb_prop *);
mhp->extlen[SADB_EXT_PROPOSAL] < sizeof(struct sadb_prop)) {
const struct sadb_prop *prop = (const struct sadb_prop *)ext;