pch_gbe: fix ip_summed checksum reporting on rx

[ Upstream commit 76a0e68129d7d24eb995a6871ab47081bbfa0acc ]

skb->ip_summed should be CHECKSUM_UNNECESSARY when the driver reports that
checksums were correct and CHECKSUM_NONE in any other case. They're
currently placed vice versa, which breaks the forwarding scenario. Fix it
by placing them as described above.

Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>