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/.gitignore b/openbsc/.gitignore
index e977f84..c57ae4b 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -66,6 +66,7 @@
 tests/si/si_test
 tests/smpp/smpp_test
 tests/bsc/bsc_test
+tests/trau/trau_test
 
 tests/atconfig
 tests/atlocal