make zram use lz4 compression algorithm

This works:

# initialize the devices
for i in $(seq ${NRDEVICES}); do
  DEVNUMBER=$((i - 1))
  echo lz4 > /sys/block/zram${DEVNUMBER}/comp_algorithm
  echo $mem > /sys/block/zram${DEVNUMBER}/disksize
  mkswap /dev/zram${DEVNUMBER}
  swapon -p 100 /dev/zram${DEVNUMBER}
done

Note: it seems you need to define the compression algorithm before zram size. Set swapon -p to priority level 100 to use zram actively as it improves performance.