Regression with revision 303970 (was kern.proc.pathname failure while booting from zfs)

[Andriy Gapon]

I've written a patch that implements zfs_vptocnp() using z_parent property.
The new code should be 100% reliable for directories and "mostly" reliable for
files (that is, when hardlinks across directories are not used).

Could you please review / test it?
https://reviews.freebsd.org/D8146

Thanks!
-- 
Andriy Gapon