no upper bound for etherbone

It occurred (using Vivado 2021.2) that, when disconnecting the fiber from a timeTransmitter
to a WR node timeReceiver, the link was not be up when re-establishing the connection.
In a disconnect situation rx_cdr_lock starts to toggle (~2x '1', 2x '0' @ 16ns) which was
undetected due to rx_cdr_lock_filtered.