3748 zfs headers should be C++ compatible
Submitted by:	Justin Gibbs <justing@spectralogic.com>
Submitted by:	Will Andrews <willa@spectralogic.com>
Reviewed by:	Matthew Ahrens <mahrens@delphix.com>
Reviewed by:	Eric Schrock <eric.schrock@delphix.com>
Reviewed by:	Robert Mustacchi <rm@joyent.com>