sky2: use correct Inter Packet Gap at 10/100mbit

This is another fix picked out of the vendor driver. The IPG value
in the serial mode register is supposed to be programmed differently
at lower speeds.

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

diff --cc drivers/net/sky2.c
Simple merge

diff --cc drivers/net/sky2.h
Simple merge