We no longer embed ifnet in softc, and the pointer to ifnet doesn't need to be first in softc now.  (It was the whole ifnet structure itself that needed to be first in the good old days.)  Fix the respective comment accordingly.
We no longer embed ifnet in softc, and the pointer to ifnet
doesn't need to be first in softc now.  (It was the whole
ifnet structure itself that needed to be first in the good
old days.)  Fix the respective comment accordingly.

Add xrefs to ifnet(9) in some other comments while I'm here.

Pointed out by:		thompsa

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