Hi halma
As is often the case there can be multiple ways of doing something under Linux. If you don't want to use udev you can try adding
this to your /opt/bootsync.sh file:
# Assign unused names to the network cards
nameif want_eth0 ab:cd:ef:12:34:56
nameif want_eth1 65:43:21:fe:dc:ba
# Assign the desired names to the network cards
nameif eth0 ab:cd:ef:12:34:56
nameif eth1 65:43:21:fe:dc:ba
If your opt directory is not persistent, run a backup and reboot. The nameif command is the busybox version of renameif.
If you do try the udev way you probably need to ad this to your /opt/bootsync.sh file:
udevadm control --reload-rules
udevadm trigger