fscache: Pass object size in rather than calling back for it

fscache: Pass object size in rather than calling back for it

Pass the object size in to fscache_acquire_cookie() and
fscache_write_page() rather than the netfs providing a callback by which it
can be received.  This makes it easier to update the size of the object
when a new page is written that extends the object.

The current object size is also passed by fscache to the check_aux
function, obviating the need to store it in the aux data.

Signed-off-by: David Howells <[email protected]>
Acked-by: Anna Schumaker <[email protected]>
Tested-by: Steve Dickson <[email protected]>