NPF_CONNKEY_V6WORDS
offsetof(npf_conn_t, c_keys[NPF_CONNKEY_V6WORDS * 2]),
#define NPF_CONNKEY_MAXWORDS (NPF_CONNKEY_V6WORDS)
KASSERT(off == NPF_CONNKEY_V4WORDS || off == NPF_CONNKEY_V6WORDS);