In its stead use the Solaris / illumos approach of emulating '-' (dash)
in probe names with '__' (two consecutive underscores).
Reviewed by: markj
MFC after: 3 weeks
existing examples to not pass an mbuf as a probe argument. There's no
obvious reason to have it there, and it doesn't really jibe with the example
added in this revision.
MFC after: 1 week
