io: convert QIOChannelBuffer to use uint8_t instead of char

The QIOChannelBuffer struct uses a 'char *' for its data
buffer. It will give simpler type compatibility with the
migration APIs if it uses 'uint8_t *' instead, avoiding
several casts.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

include/io/channel-buffer.h

@@ -42,7 +42,7 @@ struct QIOChannelBuffer {
     size_t capacity; /* Total allocated memory */
     size_t usage;    /* Current size of data */
     size_t offset;   /* Offset for future I/O ops */
-    char *data;
+    uint8_t *data;
 };