Include new storage function volume_send.

If the storage backend support import and export
we can send the contend to a remote host.

PVE/Storage/ZFSPlugin.pm

@@ -336,6 +336,13 @@ sub volume_snapshot_rollback {
     $class->zfs_add_lun_mapping_entry($scfg, $volname);
 }
 
+sub volume_send {
+    my ($class, $scfg, $storeid, $volname, $ip, $snap,
+	$incremental_snap, $verbose, $limit, $target_path) = @_;
+
+    die "Volume_send is not implemented for ZFS over iSCSI.\n";
+}
+
 sub volume_has_feature {
     my ($class, $scfg, $feature, $storeid, $volname, $snapname, $running) = @_;