rxrpc_get_rto_backoff
ktime_t rxrpc_get_rto_backoff(struct rxrpc_call *call, bool retrans);
rxrpc_get_rto_backoff(call, req.did_send);
rxrpc_get_rto_backoff(call, false));
ktime_t rto = rxrpc_get_rto_backoff(call, false);