Fix rxrpc_cleanup_ring() to use rxrpc_purge_queue() rather than
skb_queue_purge() so that the count of outstanding skbuffs is correctly
updated when a failed call is cleaned up.

Without this rmmod may hang waiting for rxrpc_n_rx_skbs to become zero.

Fixes: 5d7edbc9 ("rxrpc: Get rid of the Rx ring")
Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Eric Dumazet <edumazet@google.com>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: linux-afs@lists.infradead.org
cc: netdev@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>