move gsm_04_08_gprs.h to libosmocore

This requres the corresponding commit in libosmocore.
diff --git a/openbsc/tests/gbproxy/gbproxy_test.c b/openbsc/tests/gbproxy/gbproxy_test.c
index 96a68b0..a2ff95b 100644
--- a/openbsc/tests/gbproxy/gbproxy_test.c
+++ b/openbsc/tests/gbproxy/gbproxy_test.c
@@ -26,6 +26,7 @@
 #include <osmocom/core/rate_ctr.h>
 #include <osmocom/gsm/tlv.h>
 #include <osmocom/gsm/gsm_utils.h>
+#include <osmocom/gsm/protocol/gsm_04_08_gprs.h>
 #include <osmocom/gprs/gprs_msgb.h>
 #include <osmocom/gprs/gprs_ns.h>
 #include <osmocom/gprs/gprs_bssgp.h>
@@ -34,7 +35,6 @@
 #include <openbsc/gprs_utils.h>
 #include <openbsc/gprs_llc.h>
 #include <openbsc/gprs_gb_parse.h>
-#include <openbsc/gsm_04_08_gprs.h>
 #include <openbsc/debug.h>
 
 #include <openssl/rand.h>