Backport - EIP_AS_OPTION_MAP_SEQCOUNT for class 0 connections always mapped value zero into the DPM

This is not respected by the current implementation, nor is it tested in the current regression tests.
For class 0 connection, no sequence count is contained in the I/O frames. The user still has the possibility to map one.

Thus, we should keep track of an internal sequence count increment with each new received frame and provide it to the application as a substitute. Then, it can be used to test quickly for changes in the received data.