Move definition of MBEDTLS_CIPHER_MODE_STREAM
Move definition of `MBEDTLS_CIPHER_MODE_STREAM` to header file
(`mbedtls_cipher_internal.h`), because it is used by more than
one file. Raised by TrinityTonic in #1719
diff --git a/include/mbedtls/cipher_internal.h b/include/mbedtls/cipher_internal.h
index 6c58bcc..88baa82 100644
--- a/include/mbedtls/cipher_internal.h
+++ b/include/mbedtls/cipher_internal.h
@@ -33,6 +33,10 @@
#include "cipher.h"
+#if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER)
+#define MBEDTLS_CIPHER_MODE_STREAM
+#endif
+
#ifdef __cplusplus
extern "C" {
#endif