gtp: Use struct ul16_t/struct ul66_t to avoid compiler warnings in OsmoSGSN

This is fixing various compiler warnings:
In file included from sgsn_libgtp.c:49:0:
include/gtp.h:397:48: warning: ‘struct ul66_t’ declared inside parameter list [enabled by default]
include/gtp.h:397:48: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]
include/gtp.h:398:49: warning: ‘struct ul66_t’ declared inside parameter list [enabled by default]
include/gtp.h:399:53: warning: ‘struct ul16_t’ declared inside parameter list [enabled by default]
include/gtp.h:400:53: warning: ‘struct ul16_t’ declared inside parameter list [enabled by default]

include/gtp.h:397:48: warning: ‘struct ul66_t’ declared inside parameter list [enabled by default]
include/gtp.h:397:48: warning: its scope is only this definition or declaration, which is probably not what you want [enabled by default]
include/gtp.h:398:49: warning: ‘struct ul66_t’ declared inside parameter list [enabled by default]
include/gtp.h:399:53: warning: ‘struct ul16_t’ declared inside parameter list [enabled by default]
include/gtp.h:400:53: warning: ‘struct ul16_t’ declared inside parameter list [enabled by default]
1 file changed