netxen_nic: Fix estimation of recv MSS in case of LRO

o Linux stack estimates MSS from skb->len or skb_shinfo(skb)->gso_size.
In case of LRO skb->len is aggregate of len of number of packets hence MSS
obtained using skb->len would be incorrect. Incorrect estimation of recv MSS
would lead to delayed acks in some traffic patterns (which sends two or three
packets and wait for ack and only then send remaining packets). This leads to
drop in performance. Hence we need to set gso_size to MSS obtained from firmware.

o This is fixed recently in firmware hence the MSS is obtained based on
capability. If fw is capable of sending the MSS then only driver sets the gso_size.

Signed-off-by: Rajesh Borundia <rajesh.borundia@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>