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


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275473 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f