TRAU frame RTP conversion

This adds code that converts codec frames between (decoded) TRAU format
and RTP payload format.  The FR + EFR functions have been lifted from
OsmoNITB and exended slightly.

The HR functions have been written from scratch. There is also
incomplete code for AMR that needs to be completed + tested.

Change-Id: I7f6993cce2b95318203043e2e14952e581941b79
diff --git a/include/Makefile.am b/include/Makefile.am
index 2a99211..70f1cd6 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -6,4 +6,5 @@
  osmocom/abis/lapd.h osmocom/abis/lapd_pcap.h osmocom/trau/osmo_ortp.h	\
  osmocom/abis/unixsocket_proto.h \
  osmocom/trau/trau_frame.h \
- osmocom/trau/trau_sync.h
+ osmocom/trau/trau_sync.h \
+ osmocom/trau/trau_rtp.h