Remount datasets for "zfs inherit".

Changing properties with "zfs inherit" should cause the datasets
to be remounted. This ensures that the modified property values
will be propagated in to the filesystem namespace where they can
be enforced. This change is modeled after an identical fix made
to zfs_prop_set().

Signed-off-by: Gunnar Beutner <gunnar@beutner.name>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2201