We can make the phc2sys helper not only synchronize a PHC to
CLOCK_REALTIME, which is what it currently does, but also CLOCK_REALTIME
to a PHC, which is going to be needed in distributed TSN tests.

Instead of making the complexity of the arguments passed to
phc2sys_start() explode, we can let it figure out the sync direction
automatically, based on ptp4l's port states.

Towards that goal, pass just the path to the desired ptp4l instance's
UNIX domain socket, and remove the $if_name argument (from which it
derives the PHC). Also adapt the one caller from the ocelot psfp.sh
test. In the case of psfp.sh, phc2sys_start is able to properly figure
out that CLOCK_REALTIME is the source clock and swp1's PHC is the
destination, because of the way in which ptp4l_start for the
UDS_ADDRESS_SWP1 was called: with slave_only=false, so it will always
win the BMCA and always become the sync master between itself and $h1.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>