MFC: r217242

MFC: r217242
Fix a bug in the client side krpc where it was, sometimes
erroneously, assumed that 4 bytes of data were in the first
mbuf of a list by replacing the bcopy() with m_copydata().
Also, replace the uses of m_pullup(), which can fail for
reasons other than not enough data, with m_copydata().
For the cases where it isn't known that there is enough
data in the mbuf list, check first via m_len and m_length().
This is believed to fix a problem reported by dpd at dpdtech.com
and george+freebsd at m5p.com.

git-svn-id: svn://svn.freebsd.org/base/stable/8@217527 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f