net: dpaa: fix mode setting

net: dpaa: fix mode setting

Before converting to the phylink interface, the init function would have
set a non-reserved I/F mode in the maccfg2 register. After converting to
phylink, 0 is written as mode, which is a reserved value (although it's
the hardware default). Without a valid mode, a SGMII link is never
established between the MAC and the PHY and thus .link_up() is never
called which could set the correct mode according to the actual speed.

Fix it by setting the maximum speed of the phy_interface_t in use in
.mac_config() - just like the driver did before the phylink conversion.

Fixes: 5d93cfcf7360 ("net: dpaa: Convert to phylink")
Suggested-by: Sean Anderson <sean.anderson@linux.dev>
Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Reviewed-by: Sean Anderson <sean.anderson@linux.dev>
Link: https://patch.msgid.link/20260717132401.2653252-1-mwalle@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>