selftests: hsr: Reorder the testsuite.

Move the code and group into functions so it will be easier to extend
the test to HSRv1 so that both versions are covered.

Move the ping/test part into do_complete_ping_test() and the interface
setup into setup_hsr_interfaces().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>