6762 POSIX write should imply DELETE_CHILD on directories - and
some additional considerations

Reviewed by: Gordon Ross <gwr@nexenta.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Author: Kevin Crowe <kevin.crowe@nexenta.com>

openzfs/openzfs@d316fffc9c361532a482208561bbb614dac7f916