HSR is a redundancy protocol that duplicates traffic and sends it two
ways in a ring with an HSR header that includes a sequence number. Other
devices in the ring will forward the first occurrence of a packet, and
discard the duplicate (based on SMAC + sequence number). This enables
zero packet loss when a link goes down.

Signed-off-by: Casper Andersson <casper.casan@gmail.com>

Supervision frames are sent out by the nodes to notify about their
existence, and in the case of a RedBox it will notify about the
upstream devices.

Signed-off-by: Casper Andersson <casper.casan@gmail.com>

PRP is a redundancy protocol, like HSR, that duplicates packets and
includes a sequence number. However, PRP uses a trailer on the packet,
making the parsing a bit tricky. The trailer includes the packet size
that can be used to help ascertain it is a valid PRP trailer, however it
is still possible that this can appear naturally in a packet somewhere
in a network that doesn't use PRP.

Signed-off-by: Casper Andersson <casper.casan@gmail.com>

Test setup used:
ip link add link veth1 type veth peer name veth2
ip link set dev veth1 up
ip link set dev veth2 up
ip link add name hsr0 type hsr slave1 veth1 slave2 veth2 version 1 proto 0
ip link set dev hsr0 up

And same but with PRP:
ip link add name prp0 type hsr slave1 veth1 slave2 veth2 proto 1

Supervision frames are automatically sent out by the kernel on HSR/PRP
interfaces.

Signed-off-by: Casper Andersson <casper.casan@gmail.com>

To avoid dissecting PRP trailer when we aren't using PRP.