net: dsa: mxl862xx: reject DSA_PORT_TYPE_DSA

net: dsa: mxl862xx: reject DSA_PORT_TYPE_DSA

DSA links aren't supported by the mxl862xx driver.

Instead of returning early from .port_setup when called for
DSA_PORT_TYPE_DSA ports rather return -EOPNOTSUPP and show an error
message.

The desired side-effect is that the framework will switch the port to
DSA_PORT_TYPE_UNUSED, so we can stop caring about DSA_PORT_TYPE_DSA in
all other places.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/b686f3a22d8a6e7d470e7aa98da811a996a229b9.1775581804.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>