If we end up with a fraggap, when we copy the data
over to the next frag being built we must compute
a checksum for the bit we copy over for the new
fragment and subtract that checksum from the place
we are copying it from.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>