net: Fix typo in netdev_intersect_features

Obviously need to 'or in NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM.

Fixes: c8cd0989 ("net: Eliminate NETIF_F_GEN_CSUM and NETIF_F_V[46]_CSUM")
Reported-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>