V.42bis: integration and unit test

 - Edit previously committed V.42bis implementation to function
   outside IAXmodem.
 - Add unit test to verify the correct function of V.42bis

Change-Id: I689413f2541b6def0625ce6bd96f1f488f05f99d
diff --git a/openbsc/.gitignore b/openbsc/.gitignore
index e75b9eb..6fbd463 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -84,6 +84,7 @@
 tests/xid/xid_test
 tests/sndcp_xid/sndcp_xid_test
 tests/slhc/slhc_test
+tests/v42bis/v42bis_test
 
 tests/atconfig
 tests/atlocal