net/hsr: Add support for the High-availability Seamless Redundancy protocol (HSRv0)

High-availability Seamless Redundancy ("HSR") provides instant failover
redundancy for Ethernet networks. It requires a special network topology where
all nodes are connected in a ring (each node having two physical network
interfaces). It is suited for applications that demand high availability and
very short reaction time.

HSR acts on the Ethernet layer, using a registered Ethernet protocol type to
send special HSR frames in both directions over the ring. The driver creates
virtual network interfaces that can be used just like any ordinary Linux
network interface, for IP/TCP/UDP traffic etc. All nodes in the network ring
must be HSR capable.

This code is a "best effort" to comply with the HSR standard as described in
IEC 62439-3:2010 (HSRv0).

Signed-off-by: Arvid Brodin <arvid.brodin@xdin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>