dhcpv6.script contained support for disabling prefix delegation of 464XLAT
sub-interface, but netifd protocol handler was missing the required
export to disable this. Add missing export, akin to DS-Lite and MAP.
Signed-off-by: Lech Perczak <lech.perczak@gmail.com>
Signed-off-by: Hans Dedecker <dedeckeh@gmail.com> [PKG_RELEASE increase]