be2net: reduce gso_max_size setting to account for ethernet header.

The maximum size of packet that can be handled by controller including ethernet
header is 65535. Reducing gso_max_size accordingly.

Signed-off-by: Sarveshwar Bandi <sarveshwar.bandi@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>