"eth0" is old device naming. The IoT devkit image uses the current scheme (whereas the built-in Yocto is slightly older and uses old naming scheme). If you type "ifconfig" without parameters (or the newer command "ip a" - ifconfig only there for legacy reasons) you should find the "enp..." device which is the ethernet controller.
If you insist in having the naming to "eth0" you can modify the behavior - I think it's a udev rule you'd have to change. Check the web for that
On telnetd - well, the images are different. What do you need telnetd for? Maybe you could use "nc"?
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