Add zfs module feature and property compatibility

This change is required to ease the transition when upgrading
from 0.7.x to 0.8.x. It allows 0.8.x user space utilities to
remain compatible with 0.7.x and older kernel modules.

Reviewed-by: Don Brady <don.brady@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #8231