net: convert sunrpc from pagevec to folio_batch

Remove the last usage of pagevecs.  There is a slight change here; we now
free the folio_batch as soon as it fills up instead of freeing the
folio_batch when we try to add a page to a full batch.  This should have
no effect in practice.

Link: https://lkml.kernel.org/r/20230621164557.3510324-10-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>