ifb: fix packets checksum

Fixup the checksum for CHECKSUM_COMPLETE when pulling skbs on RX path.
Otherwise we get splats when tc mirred is used to redirect packets to ifb.

Before fix:

nic: hw csum failure

Signed-off-by: Jon Maxwell <jmaxwell37@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>