botan: Extract helper function to map RNG quality to Botan RNG names

src/libstrongswan/plugins/botan/botan_rng.c

@@ -22,6 +22,7 @@
  */
 
 #include "botan_rng.h"
+#include "botan_util.h"
 
 #include <botan/build.h>
 
@@ -83,29 +84,12 @@ METHOD(rng_t, destroy, void,
 botan_random_t *botan_rng_create(rng_quality_t quality)
 {
 	private_botan_random_t *this;
-	const char* rng_name;
+	const char *rng_name;
 
-	switch (quality)
+	rng_name = botan_map_rng_quality(quality);
+	if (!rng_name)
 	{
-		case RNG_WEAK:
-		case RNG_STRONG:
-			/* some rng_t instances of this class (e.g. in the ike-sa-manager)
-			 * may be called concurrently by different threads. the Botan RNGs
-			 * are not reentrant, by default, so use the threadsafe version.
-			 * because we build without threading support when running tests
-			 * with leak-detective (lots of reports of frees of unknown memory)
-			 * there is a fallback to the default */
-#ifdef BOTAN_TARGET_OS_HAS_THREADS
-			rng_name = "user-threadsafe";
-#else
-			rng_name = "user";
-#endif
-			break;
-		case RNG_TRUE:
-			rng_name = "system";
-			break;
-		default:
-			return NULL;
+		return NULL;
 	}
 
 	INIT(this,