Linux 3.6 compat, iops->lookup()

As of Linux commit 00cd8dd3bf95f2cc8435b4cac01d9995635c6d0b the
struct nameidata is no longer passed to iops->lookup. Instead
only the inamedata->flags are passed.

ZFS like almost all Linux fileystems never made use of this so
only the prototype needs to be wrapped for compatibility.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #873