selftests: Add a basic HSR test.

This test adds a basic HSRv0 network with 3 nodes. In its current shape
it sends and forwards packets, announcements and so merges nodes based
on MAC A/B information.
It is able to detect duplicate packets and packetloss should any occur.

Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>