BUG/MINOR: fct peer_prepare_ackmsg should not use trash.

function 'peer_prepare_ackmsg' is designed to use the argument 'msg'
instead of 'trash.str'.

There is currently no bug because the caller passes 'trash.str' in
the 'msg' argument.

src/peers.c

@@ -417,7 +417,7 @@ static int peer_prepare_ackmsg(struct shared_table *st, char *msg, size_t size)
 	char *cursor, *datamsg;
 	uint32_t netinteger;
 
-	cursor = datamsg = trash.str + 2 + 5;
+	cursor = datamsg = msg + 2 + 5;
 
 	intencode(st->remote_id, &cursor);
 	netinteger = htonl(st->last_get);