LU-11507 osd-zfs: Use zfs_refcount_add if available

LU-11507 osd-zfs: Use zfs_refcount_add if available

refcount_add was removed from ZFS master in:

    Linux 4.19-rc3+ compat: Remove refcount_t compat
    https://github.com/zfsonlinux/zfs/pull/7932

It is expected to be removed in zfs-0.7.12 as well.  Update Lustre
to use zfs_refcount_add if zfs supports it, and fall back to
refcount_add if not.

Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Change-Id: Ib1b2ff13eb4ff8c56dd49a427b9827c6649ecd31
Reviewed-on: https://review.whamcloud.com/33359
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Nathaniel Clark <nclark@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>