RXRPC_KEEPALIVE_TIME
diff = clamp(diff, -RXRPC_KEEPALIVE_TIME, RXRPC_KEEPALIVE_TIME);
keepalive_at = rxrpc_peer_get_tx_mark(peer, base) + RXRPC_KEEPALIVE_TIME;
keepalive_at > base + RXRPC_KEEPALIVE_TIME) {
slot = RXRPC_KEEPALIVE_TIME;
stop = cursor + RXRPC_KEEPALIVE_TIME - 1;