Create new specific file for BSSGP code

Right now there's no much code there since the related code is totally
entangled with the LLC one.
This will eventually change in the future when we switch to use
libosmo-gprs.
Hence, this commit is a preparation to have already some place to put
new BSSGP specific code in the future.

Change-Id: I816396ab5ccb86032bbc21b41a959934a7768780
diff --git a/include/osmocom/sgsn/Makefile.am b/include/osmocom/sgsn/Makefile.am
index 515c79c..3b1f840 100644
--- a/include/osmocom/sgsn/Makefile.am
+++ b/include/osmocom/sgsn/Makefile.am
@@ -2,6 +2,7 @@
 	common.h \
 	crc24.h \
 	debug.h \
+	gprs_bssgp.h \
 	gprs_gb.h \
 	gprs_gmm.h \
 	gprs_gmm_fsm.h \
diff --git a/include/osmocom/sgsn/gprs_bssgp.h b/include/osmocom/sgsn/gprs_bssgp.h
new file mode 100644
index 0000000..0feaa97
--- /dev/null
+++ b/include/osmocom/sgsn/gprs_bssgp.h
@@ -0,0 +1,12 @@
+#pragma once
+
+#include <osmocom/core/msgb.h>
+
+/* Called by bssgp layer when a prim is received from lower layers. */
+int sgsn_bssgp_rx_prim(struct osmo_prim_hdr *oph);
+
+/* called by the bssgp layer to send NS PDUs */
+int sgsn_bssgp_dispatch_ns_unitdata_req_cb(void *ctx, struct msgb *msg);
+
+/* page a MS in its routing area */
+int sgsn_bssgp_page_ps_ra(struct sgsn_mm_ctx *mmctx);
diff --git a/include/osmocom/sgsn/gprs_gb.h b/include/osmocom/sgsn/gprs_gb.h
index 9162367..e39ebc6 100644
--- a/include/osmocom/sgsn/gprs_gb.h
+++ b/include/osmocom/sgsn/gprs_gb.h
@@ -10,11 +10,5 @@
 /* Has to be called whenever any PDU (signaling, data, ...) has been received */
 void gprs_gb_recv_pdu(struct sgsn_mm_ctx *mmctx, const struct msgb *msg);
 
-/* page a MS in its routing area */
-int gprs_gb_page_ps_ra(struct sgsn_mm_ctx *mmctx);
-
-/* called by the bssgp layer to send NS PDUs */
-int gprs_gb_send_cb(void *ctx, struct msgb *msg);
-
 /* called by the ns layer */
 int gprs_ns_prim_cb(struct osmo_prim_hdr *oph, void *ctx);