update_sharetab() should open the file as writable.
Accidentally used the 'r' mode!
* Minor comment changes.
* Use 'dataset' instead of 'path' in call to iscsi_generate_target().
* Remove assert() from iscsi_generate_target(). They are empty in call and set during the function.
* In iscsi_disable_share_all(), check the return value from iscsi_disable_share_one().
* Remove iscsi_retrieve_targets() call in iscsi_is_share_active(). Unnessesary.