MFC 253656: Enhance the description of NOTE_TRACK:
- NOTE_TRACK has never triggered a NOTE_TRACK event from the parent pid.
  If NOTE_FORK is set, the listener will get a NOTE_FORK event from
  the parent pid, but not a separate NOTE_TRACK event.
- Explicitly note that the event added to monitor the child process
  preserves the fflags from the original event.
- Move the description of NOTE_TRACKERR under NOTE_TRACK as it is not a
  bit for the user to set (which is what this list pupports to be).
  Also, explicitly note that if an error occurs, the NOTE_CHILD event
  will not be generated.
MFC r257539:

When zero'ing out a buffer, make sure we are using right size.

Without this change, in the worst but unlikely case scenario, certain
administrative operations, including change of configuration, set or
delete key from a GEOM ELI provider, may leave potentially sensitive
information in buffer allocated from kernel memory.

We believe that it is not possible to actively exploit these issues, nor
does it impact the security of normal usage of GEOM ELI providers when
these operations are not performed after system boot.

Security:	possible sensitive information disclosure
Submitted by:	Clement Lecigne <clecigne google com>