Replace ZoL with OpenZFS where applicable

Replace ZoL with OpenZFS where applicable

Afterward, git grep ZoL matches:
  * README.md:  * [ZoL Site](https://zfsonlinux.org)
  - Correct
  * etc/default/zfs.in:# ZoL userland configuration.
  - Changing this would induce a needless upgrade-check,
    if the user has modified the configuration;
    this can be updated the next time the defaults change
  * module/zfs/dmu_send.c:   * ZoL < 0.7 does not handle [...]
  - Before 0.7 is ZoL, so fair enough

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Issue #11956