zfs: auto import after reboot

this is necessary, because after a reboot all pools except rpool are gone

Signed-off-by: Wolfgang Link <w.link@proxmox.com>

PVE/Storage/ZFSPlugin.pm

@@ -350,4 +350,9 @@ sub volume_has_feature {
     return undef;
 }
 
+sub activate_storage {
+    my ($class, $storeid, $scfg, $cache) = @_;
+    return 1;
+}
+
 1;