common labels for LINT. There are still some common declarations for the
!KERNEL case in tcp_debug.h and spx_debug.h. trpt depends on the ones in
tcp_debug.h.
- fill in and use ifp->if_softc
- use if_bpf rather than private cookie variables
- change bpf interface to take advantage of this
- call ether_ifattach() directly from Ethernet drivers
- delete kludge in if_attach() that did this indirectly
