Revert "Took out now-obsolete preCommitHook from gasharl interfaceCustom"

This reverts commit 44e60d013704317d9820fcbfe68d5b2199657d73.
Made the correct change to preCommitHook on gasharl interfaceCustom

We do want to null out an interface's ethernet info (MAC address)
field if the IP net we're connected to doesn't want MAC addresses
registered.. we just don't need to manually re-do the label, as that
will be done for us by the setFieldValueLocal on ETHERNETINFO.