libmsc: Use RAND_bytes when choosing a tmsi

Require openssl version to be >= 0.9.5 because we rely on the RAND_bytes
return value.

[hfreyther: Add cast to uint8_t*]
diff --git a/openbsc/tests/channel/Makefile.am b/openbsc/tests/channel/Makefile.am
index 519efbd..51b2f83 100644
--- a/openbsc/tests/channel/Makefile.am
+++ b/openbsc/tests/channel/Makefile.am
@@ -11,4 +11,4 @@
 	$(top_builddir)/src/libmsc/libmsc.a \
 	$(top_builddir)/src/libcommon/libcommon.a \
 	$(LIBOSMOCORE_LIBS) \
-	-ldbi $(LIBOSMOGSM_LIBS)
+	-ldbi $(LIBOSMOGSM_LIBS) $(LIBCRYPTO_LIBS)