net: i82596: fix dma_alloc_attr for sni_82596

Commit 7f683b92 ("i825xx: switch to switch to dma_alloc_attrs")
switched dma allocation over to dma_alloc_attr, but didn't convert
the SNI part to request consistent DMA memory. This broke sni_82596
since driver doesn't do dma_cache_sync for performance reasons.
Fix this by using different DMA_ATTRs for lasi_82596 and sni_82596.

Fixes: 7f683b92 ("i825xx: switch to switch to dma_alloc_attrs")
Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>