Use m_uiotombuf() instead of own implementation. This is not just
a cosmetic change. m_uiotombuf() produces a packet header mbuf, while
original implementation did not. When kernel is compiled with MAC
support, headerless mbuf will cause panic.

Reported by: Alexander Nikiforenko <asn rambler-co.ru>
Approved by: re (scottl)
MFC After: 2 weeks