sfc: Specify that the VFDI status page has page alignment and size

This requirement was meant to be implied in the name 'status page'.
One out-of-tree VF driver allocates a buffer using the structure size
and not a full page - hence the current odd specification - but in
practice that allocation will be padded and aligned to at least 4KB.
Therefore, we can specify this and have the option to extend the
structure up to 4KB without worrying about VF drivers using odd-shaped
buffers.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/vfdi.h

@@ -152,7 +152,8 @@ enum vfdi_op {
  *	all traffic at this receive queue.
  * @u.mac_filter.flags: MAC filter flags.
  * @u.set_status_page.dma_addr: Base address for the &struct vfdi_status.
- *	This address must be such that the structure fits within a page.
+ *	This address must be page-aligned and the PF may write up to a
+ *	whole page (allowing for extension of the structure).
  * @u.set_status_page.peer_page_count: Number of additional pages the VF
  *	has provided into which peer addresses may be DMAd.
  * @u.set_status_page.peer_page_addr: Array of DMA addresses of pages.