Properly set and save dataset inherit values in new UI

Compression level, deduplication and readonly are set to “Inherit” (see screenshot) on a dataset. However, after saving the source is set to “local” instead of “inherited from tank”:

root@freenas[~]# zfs get compression tank/work/mhp-data
NAME                PROPERTY     VALUE     SOURCE
tank/work/mhp-data  compression  lz4       local