MFH r230580:
Don't mention no longer supported ioctl commands.

MFH r274083:
convert .Nm to proper .Xr's...

MFH r275298:
Cross reference tap(4) and tun(4) and include a short explanation as
to how they differ. This will assist users in selecting which interface
is more appropriate for their purposes.

No objection: glebius (r230580), jmg (r274083)
Approved by: grog (co-mentor)