Feature: Support DLR V3 services "Learning_Update" and "Flush_Tables"

In revision 3 of the DLR object basically the new redundant gateway functionality is defined, which the Hilscher stack will not support.

However, this extention comes with two new frame types that need to be handled/sent by the stack:

Flush_Table frame:
The Flush_Tables frame is sent by the new active gateway to indicate that DLR nodes should flush their unicast and multicast MAC address learning tables.

Learning_Update frame:
The Learning_Update frame is sent by all DLR nodes upon receiving a Flush_Tables frame from active gateway and if Learning Update Enable field is set to TRUE to accelerate learning of new network topology by non-DLR switches outside of DLR network.

The state machine of the beacon based DLR device is therefore extended by two entries. See table Table 9-5.21 Event No. 47 and 48 (CIP Vol2_1.14).