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/tests/Makefile.am b/openbsc/tests/Makefile.am
index 7f51bfa..d4bb954 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -1,4 +1,4 @@
-SUBDIRS = gsm0408 db channel mgcp gprs si abis gbproxy
+SUBDIRS = gsm0408 db channel mgcp gprs si abis gbproxy trau
 
 if BUILD_NAT
 SUBDIRS += bsc-nat bsc-nat-trie