myr10ge: again fix lro_gen_skb() alignment

Add LRO alignment initially committed in
621544eb ("[LRO]: fix lro_gen_skb()
alignment") and removed in 0dcffac1
("myri10ge: add multislices support") during conversion to
multi-slice.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>