sfc: Fix reading non-legacy supported link modes

Everything except the first 32 bits was lost when the pause flags were
added. This makes the 50000baseCR2 mode flag (bit 34) not appear.

I have tested this with a 10G card (SFN5122F-R7) by modifying it to
return a non-legacy link mode (10000baseCR).

Signed-off-by: Erik Ekman <erik@kryo.se>
Signed-off-by: David S. Miller <davem@davemloft.net>