Now that if_input() set the receiving interface pointer on mbufs for us

Now that if_input() set the receiving interface pointer on mbufs for us
there's no need to do it in m_devget(9).

Stop passing an ``ifp'' will help for upcoming interface pointer -> index
conversion.

While here remove unused ``ifp'' argument from m_clget(9) and kill two
birds^W layer violations in one commit.

ok henning@