Rename internal header constant_time.h to constant_time_internal.h

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 58f41be..59cb9d2 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -44,7 +44,7 @@
 #include "mbedtls/error.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/version.h"
-#include "constant_time.h"
+#include "constant_time_internal.h"
 #include "mbedtls/constant_time.h"
 
 #include <string.h>