move OAP messages implementations to libosmocore

This corresponds to change-id If5099e60681a215e798b6675f21813f26769c253 in
libosmocore, which is now required to build openbsc.

Related: OS#1592
Change-Id: I2f06aaa6eb54eafa860cfed8e72e41d82ff1c4cf
diff --git a/openbsc/src/gprs/oap.c b/openbsc/src/gprs/oap.c
index c7c9777..7efbe81 100644
--- a/openbsc/src/gprs/oap.c
+++ b/openbsc/src/gprs/oap.c
@@ -24,10 +24,10 @@
 
 #include <osmocom/core/utils.h>
 #include <osmocom/crypt/auth.h>
+#include <osmocom/gsm/oap.h>
 
 #include <openbsc/oap.h>
 #include <openbsc/debug.h>
-#include <openbsc/oap_messages.h>
 
 int oap_init(struct oap_config *config, struct oap_state *state)
 {