abis: Create a routine that can parse all SW Descriptions of a SW Config

Be able to parse the entire SW Config IE. Parse the SW Descruption
into a struct provided by the caller.
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 1bb660f..91ae08a 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -151,6 +151,7 @@
     tests/mgcp/Makefile
     tests/gprs/Makefile
     tests/si/Makefile
+    tests/abis/Makefile
     doc/Makefile
     doc/examples/Makefile
     Makefile)