cipher: handle ChaCha20 as a stream cipher
That's what it is. So we shouldn't set a block size != 1.
While at it, move call to chachapoly_update() closer to the one for GCM, as
they are similar (AEAD).
diff --git a/include/mbedtls/cipher.h b/include/mbedtls/cipher.h
index 591aa79..1ae847d 100644
--- a/include/mbedtls/cipher.h
+++ b/include/mbedtls/cipher.h
@@ -193,7 +193,7 @@
/** Maximum length of any IV, in Bytes. */
#define MBEDTLS_MAX_IV_LENGTH 16
/** Maximum block size of any cipher, in Bytes. */
-#define MBEDTLS_MAX_BLOCK_LENGTH 64
+#define MBEDTLS_MAX_BLOCK_LENGTH 16
/**
* Base cipher information (opaque struct).