tc filter for small udp packets < 64 bytes

Hi guys, according  to http://lartc.org/howto/lartc.adv-filter.html i
can use the following filter  to match ACKs on packets smaller than 64
bytes:
        tc filter add dev $interface parent 1:0 protocol ip prio 1 u32 \
            match ip protocol 6 0xff \
            match u8 0x05 0x0f at 0 \
            match u16 0x0000 0xffc0 at 2 \
            match u8 0x10 0xff at 33 \
            flowid 1:10

but how can i filter any udp packet smaller than 64 bytes?



[]'s
Salatiel