Add EFR support to TRAU muxer + test case

Decoding and encoding of FR and EFR TRAU frames are put into seperate
functions. CRC check is done to detect bad EFR TRAU frames.

The test case includes FR and EFR transcoding.

EFR support was tested with Nokia InSite BTS and Siemens BS11.
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 081e416..fe99569 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -169,6 +169,7 @@
     tests/si/Makefile
     tests/abis/Makefile
     tests/smpp/Makefile
+    tests/trau/Makefile
     doc/Makefile
     doc/examples/Makefile
     Makefile)