Sync /dev/zfs ioctl ordering

In order to minimize any future disruption caused by the addition
and removal /dev/zfs ioctls this patch makes the following changes.

1) Sync ZoL's ioctl ordering such that it matches Illumos.  For
   historic reasons the ZFS_IOC_DESTROY_SNAPS and ZFS_IOC_POOL_REGUID
   ioctls were out of order.

2) Move Linux and FreeBSD specific ioctls in to their own reserved
   ranges.  This allows us to preserve the existing ordering when
   new ioctls are added by either Illumos or FreeBSD.  When an
   ioctl is no longer needed it should be retired in place.

This change alters the ZFS user/kernel ABI so make sure you rebuild
both your user and kernel modules.  However, it should allow for a
much stabler interface going forward.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1973