wg_pkt_data
(offsetof(struct wg_pkt_data, buf[(n)]) + NOISE_AUTHTAG_LEN)
struct wg_pkt_data *data;
M_PREPEND(m, sizeof(struct wg_pkt_data), M_NOWAIT);
data = mtod(m, struct wg_pkt_data *);
pkt->p_counter = le64toh(mtod(m, struct wg_pkt_data *)->counter);
m_adj(m, sizeof(struct wg_pkt_data));
struct wg_pkt_data *data;
pkt->p_mbuf = m_pullup(m, sizeof(struct wg_pkt_data));
data = mtod(pkt->p_mbuf, struct wg_pkt_data *);