Check whether deltas (delta_tx_m, delta_rx_m, delta_tx_s, delta_rx_s) are
not zero in SNMP, not in PPSI

Remove object wrsPtpRTTErrCnt from MIB, not compatible change, but we're before
release...

Update PPSI
Signed-off-by: Adam Wujek <adam.wujek@cern.ch>