Changes

gtp: remove unused conversion functions

Remove ipv42eua and eua2ipv4, which are in the "internal functions"
section of gtp.h, but are not used anywhere in the code anymore. This is
in preparation of moving the internal functions that are used in
multiple .c files into a separate header file, and to make the other
internal functions static. (Compiler complains about unused static
functions.)

Change-Id: I90e2750f6a6e3e6122e9c562103fda77d7326932