For the M_PREPEND macro, remove an initial mbuf NULL check I added.  It was added accidentally, and although not terrible, it would improperly hide the bug of calling M_PREPEND with a NULL mbuf argument.
For the M_PREPEND macro, remove an initial mbuf NULL check I added.  It
was added accidentally, and although not terrible, it would improperly
hide the bug of calling M_PREPEND with a NULL mbuf argument.

Submitted by:	jlemon (ISTR)

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase