net: dsa: felix: allow PHY_INTERFACE_MODE_INTERNAL on port 5

net: dsa: felix: allow PHY_INTERFACE_MODE_INTERNAL on port 5

The Felix switch has 6 ports, 2 of which are internal.
Due to some misunderstanding, my initial suggestion for
vsc9959_port_modes[]:
https://patchwork.kernel.org/project/netdevbpf/patch/20220129220221.2823127-10-colin.foster@in-advantage.com/#24718277

got translated by Colin into a 5-port array, leading to an all-zero port
mode mask for port 5.

Fixes: b19dd43419dd ("net: dsa: felix: remove prevalidate_phy_mode interface")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220318195812.276276-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>