netfs: Use a folio_queue allocation and free functions

Provide and use folio_queue allocation and free functions to combine the
allocation, initialisation and stat (un)accounting steps that are repeated
in several places.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241216204124.3752367-4-dhowells@redhat.com


cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>