net: mvpp2: fix detection of 10G SFP modules

The mvpp2_phylink_validate() relies on the interface field of
phylink_link_state to determine valid link modes. However, when called
from phylink_sfp_module_insert() this field in not initialized. The
default switch case then excludes 10G link modes. This allows 10G SFP
modules that are detected correctly to be configured at max rate of
2.5G.

Catch the uninitialized PHY mode case, and allow 10G rates.

Fixes: d97c9f4a ("net: mvpp2: 1000baseX support")
Cc: Maxime Chevallier <maxime.chevallier@bootlin.com>
Cc: Antoine Tenart <antoine.tenart@bootlin.com>
Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>