example:
```sh
❯ docker run --rm -ti alpine
/ # KOPT_blacklist=igb,ixgbe,tg3
/ # for i in ${KOPT_blacklist/,/ }; do echo "blacklist $i"; done
blacklist igb
blacklist ixgbe,tg3
/ # for i in ${KOPT_blacklist//,/ }; do echo "blacklist $i"; done
blacklist igb
blacklist ixgbe
blacklist tg3
```