Argon Device OS MTU size for Featherwing

The MTU (Maximum Transmission Unit) for Ethernet, for instance, is 1500 bytes but Ubuntu is sending 1514 bytes. I’ve increased buffer size in code.ino to 1550 for but no success on 1460 byte TCP frame (which is 1514 bytes Ethernet). I searched back an couldn’t find a apecific answer. I’m a newbie to this forum so do I need to start reading Device OS code from Github or is there some other way of finding such answer?