nulldriver - Null driver
This driver succeeds probe(9E), attach(9E)
and detach(9E) but provides no namespace or functionality.
In some circumstances having device nodes bound to nulldriver is expected. For example, prtconf(1M) might capture a nexus driver with
a nulldriver bound child if the nexus is performing child discovery.
prtconf(1M), attach(9E), detach(9E), probe(9E)