staging/octeon: Software should check the checksum of no tcp/udp packets
Icmp packets with wrong checksum are never dropped since skb->ip_summed is
set to CHECKSUM_UNNECESSARY.
When icmp packets with wrong checksum pass through the octeon net driver,
the not_IP, IP_exc, L4_error hardware indicators show no error. so the
driver sets CHECKSUM_UNNECESSARY on skb->ip_summed.