[rtp] Describe the struct in a way that it will work for Big Endian too

Play with the right bits on PPC.
diff --git a/openbsc/src/rtp_proxy.c b/openbsc/src/rtp_proxy.c
index 9b1f4d9..9f2e2fd 100644
--- a/openbsc/src/rtp_proxy.c
+++ b/openbsc/src/rtp_proxy.c
@@ -19,6 +19,7 @@
  *
  */
 
+#include <endian.h>
 #include <errno.h>
 #include <unistd.h>
 #include <sys/socket.h>
@@ -63,12 +64,21 @@
 
 /* according to RFC 3550 */
 struct rtp_hdr {
+#if __BYTE_ORDER == __LITTLE_ENDIAN
 	u_int8_t  csrc_count:4,
 		  extension:1,
 		  padding:1,
 		  version:2;
 	u_int8_t  payload_type:7,
 		  marker:1;
+#elif __BYTE_ORDER == __BIG_ENDIAN
+	u_int8_t  version:2,
+		  padding:1,
+		  extension:1,
+		  csrc_count:4;
+	u_int8_t  marker:1,
+		  payload_type:7;
+#endif
 	u_int16_t sequence;
 	u_int32_t timestamp;
 	u_int32_t ssrc;