afs: Use peer + service_id as call address

Use the rxrpc_peer plus the service ID as the call address instead of
passing in a sockaddr_srx down to rxrpc.  The peer record is obtained by
using rxrpc_kernel_get_peer().  This avoids the need to repeatedly look up
the peer and allows rxrpc to hold on to resources for it.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org