node: add flags to port_use_buffer

Remove the CAN_USE_BUFFERS flag, it is redundant. We can know this
because of the IO params and buffer params.

Add flags to the port_use_buffer call. We also want this call to
replace port_alloc_buffer. Together with a new result event we can
ask the node to (a)synchronously fill up the buffer data for us. This
is part of a plan to let remote nodes provide buffer data.

spa/plugins/v4l2/v4l2-source.c

@@ -678,6 +678,7 @@ static int impl_node_port_set_param(void *object,
 static int impl_node_port_use_buffers(void *object,
 				      enum spa_direction direction,
 				      uint32_t port_id,
+				      uint32_t flags,
 				      struct spa_buffer **buffers,
 				      uint32_t n_buffers)
 {