etc: mask zfs-load-key.service

Otherwise, systemd-sysv-generator will generate a service equivalent
that breaks the boot: under systemd this is covered by
zfs-mount-generator

We already do this for zfs-import.service, and other init scripts are
suppressed automatically by the "actual" .service files

Fixes: commit f04b976 ("Add init script
 to load keys")
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#14010
Closes openzfs#14019

etc/Makefile.am

@@ -74,6 +74,7 @@ INSTALL_DATA_HOOKS += systemd-install-data-hook
 systemd-install-data-hook:
 	$(MKDIR_P) "$(DESTDIR)$(systemdunitdir)"
 	ln -sf /dev/null "$(DESTDIR)$(systemdunitdir)/zfs-import.service"
+	ln -sf /dev/null "$(DESTDIR)$(systemdunitdir)/zfs-load-key.service"
 
 
 systemdgenerator_PROGRAMS = \