lagg_m_extract
eh = lagg_m_extract(m, 0, sizeof(*eh), __alignof(*eh), &buf);
evl = lagg_m_extract(m, 0, sizeof(*evl), __alignof(*evl),
ip = lagg_m_extract(m, off, sizeof(*ip), __alignof(*ip), &buf);
ip6 = lagg_m_extract(m, off, sizeof(*ip6), __alignof(*ip6),
th = lagg_m_extract(m, off, sizeof(*th), __alignof(*th), &buf);
uh = lagg_m_extract(m, off, sizeof(*uh), __alignof(*uh), &buf);