Changes

gtp/gtp.c: move gtp_create_context_resp down

Move gtp_create_context_resp below gtp_create_pdp_resp, which it calls.
In a follow-up commit, we can make gtp_create_pdp_resp static and
remove the additional declaration.

Change-Id: I34efe7592013a8423f4f280758272d81f24b65fa