[mgcp] Export header parsing via mgcp internal

This will be used by the NAT code to implement custom protocol
handling on top of that.
diff --git a/openbsc/include/openbsc/mgcp_internal.h b/openbsc/include/openbsc/mgcp_internal.h
index 10d0ca6..7ce1732 100644
--- a/openbsc/include/openbsc/mgcp_internal.h
+++ b/openbsc/include/openbsc/mgcp_internal.h
@@ -61,4 +61,13 @@
 
 #define ENDPOINT_NUMBER(endp) abs(endp - endp->cfg->endpoints)
 
+struct mgcp_msg_ptr {
+	unsigned int start;
+	unsigned int length;
+};
+
+int mgcp_analyze_header(struct mgcp_config *cfg, struct msgb *msg,
+			struct mgcp_msg_ptr *ptr, int size,
+			const char **transaction_id, struct mgcp_endpoint **endp);
+
 #endif