Fix another dependency loop

zfs-load-key-DATASET.service was gaining an
After=systemd-journald.socket due to its stdout/stderr going to the
journal (which is the default).  systemd-journald.socket has an After
(via RequiresMountsFor=/run/systemd/journal) on -.mount.  If the root
filesystem is encrypted, -.mount gets an After
zfs-load-key-DATASET.service.

By setting stdout and stderr to null on the key load services, we avoid
this loop.

Signed-off-by: Richard Laager <[email protected]>

Author: rlaager

etc/systemd/system-generators/zfs-mount-generator.in

@@ -212,6 +212,10 @@ ${keymountdep}
 [Service]
 Type=oneshot
 RemainAfterExit=yes
+# This avoids a dependency loop involving systemd-journald.socket if this
+# dataset is a parent of the root filesystem.
+StandardOutput=null
+StandardError=null
 ExecStart=${keyloadcmd}
 ExecStop=@sbindir@/zfs unload-key '${dataset}'"   > "${dest_norm}/${keyloadunit}"
     fi