sky2: align IP header on Rx if possible

The sky2 driver was not aligning the IP header on receive buffers.
This workaround is only needed on hardware with broken FIFO, newer chips
without FIFO can just DMA to unaligned address.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>