hsr: Follow standard for HSRv0 supervision frames

hsr: Follow standard for HSRv0 supervision frames

For HSRv0, the path_id has the following meaning:
- 0000: PRP supervision frame
- 0001-1001: HSR ring identifier
- 1010-1011: Frames from PRP network (A/B, with RedBoxes)
- 1111: HSR supervision frame

Follow the IEC 62439-3:2010 standard more closely by setting the right
path_id for HSRv0 supervision frames (actually, it is correctly set when
the frame is constructed, but hsr_set_path_id() overwrites it) and set a
fixed HSR ring identifier of 1. The ring identifier seems to be generally
unused and we ignore it anyways on reception, but some fixed identifier is
definitely better than using one identifier in one direction and a wrong
identifier in the other.

This was also the behavior before commit f266a683a480 ("net/hsr: Better
frame dispatch") which introduced the alternating path_id. This was later
moved to hsr_set_path_id() in commit 451d8123f897 ("net: prp: add packet
handling support").

The IEC 62439-3:2010 also contains 6 unused bytes after the MacAddressA in
the HSRv0 supervision frames. Adjust a TODO comment accordingly.

Fixes: f266a683a480 ("net/hsr: Better frame dispatch")
Fixes: 451d8123f897 ("net: prp: add packet handling support")
Signed-off-by: Felix Maurer <fmaurer@redhat.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/ea0d5133cd593856b2fa673d6e2067bf1d4d1794.1762876095.git.fmaurer@redhat.com
Tested-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>