Use value_string for ctrl_type

Use value_string for enum ctrl_type instead of custom code. Add
corresponding unit tests.

Related: OS#1615
Change-Id: Icd4e96dd9f00876cb70b43cfcf42ab4f10311b28
diff --git a/.gitignore b/.gitignore
index ad8354e..48642ca 100644
--- a/.gitignore
+++ b/.gitignore
@@ -59,7 +59,7 @@
 tests/testsuite
 tests/testsuite.dir/
 tests/testsuite.log
-
+tests/ctrl/ctrl_test
 tests/utils/utils_test
 tests/stats/stats_test
 tests/kasumi/kasumi_test