There's no need to clear the Info column right before setting it; we
don't use any information from the packet other than stuff we've already
determined is there (as part of the heuristic test for a DCE RPC
packet), so there's no risk that we'll throw an exception before the
Info column is set.
Use "col_set_str()", rather than "col_add_str()" or "col_add_fstr()", to
set the Protocol and Info columns.
svn path=/trunk/; revision=3145
Guy Harris