Fix switch port diagnosis counters

In the current implementation the "In-Discards" counter of a switch port returns the number of frames discarded on reception due to Port State "Discard/Blocked".

According to Profinet Specification the "In-Discards" counter shall count "The number of received valid frames (from the sublayer below), which could not be delivered to the sublayer above because of missing resources.". This corresponds to frames dropped due resource reasons not due port state.

The implementation needs to be fixed to behave as required. Other counters should be checked as well.