afs: Fix callback service message parsers to pass through -EAGAIN

afs: Fix callback service message parsers to pass through -EAGAIN

The AFS filesystem client uses an rxrpc server to listen for callback
notifications.  Each callback call type handler has a delivery function
that parses the incoming request stream, and this should return -EAGAIN the
last packet hasn't yet been seen, but all currently queued received data is
consumed.  afs_extract_data() does this, but the -EAGAIN return is switched
to 0 inadvertantly

Fix callback service message parsers to pass through -EAGAIN

Fixes: d001648ec7cf ("rxrpc: Don't expose skbs to in-kernel users [ver #2]")
Closes: https://sashiko.dev/#/patchset/20260609081738.770127-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260622090856.2746629-14-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>