This is a small standalone program (under MIT license, hence cannot make
use of libosmocore) whose only purpose is to answer GTPC (v1 and v2)
Echo Request messages with Echo Reply ones, with information provided
from the command line.
A small python script companion is provided to easily test the program.
Related: SYS#5598
Change-Id: Ibdd6d8f6920571db0c60cf8b3b25d541b15ad3f1
