core/conv: Add regression testing code

It tests both a given test vector encoding/decoding, and
some random coding/decoding cycles.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/configure.ac b/configure.ac
index 450ccd3..b505eb1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -165,6 +165,7 @@
 	tests/smscb/Makefile
 	tests/bits/Makefile
 	tests/a5/Makefile
+	tests/conv/Makefile
 	utils/Makefile
 	Doxyfile.core
 	Doxyfile.gsm