sky2: fix pause negotiation

The sky2 driver combines auto speed negotiation with automatic negotiation
of pause parameters; but the ethtool interface expects them to be
split. This patch allows autonegotiation to be used for speed, but
manually disable flow control.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>