Fix style(9) and remove m_freem(NULL).
Add XXX comment, it looks incorrect, because m_pkthdr.len is already
incremented by M_PREPEND().

Sponsored by:	Yandex LLC
Merge remote-tracking branch 'freebsd/master' into hardened/current/master
Merge remote-tracking branch 'origin/hardened/current/master' into hardened/current/unstable