Revert "net: Handle CHECKSUM_COMPLETE more adequately in pskb_trim_rcsum()."

Revert "net: Handle CHECKSUM_COMPLETE more adequately in pskb_trim_rcsum()."

This reverts commit b50281c5164a7549c45c29e2b63bb01a0ce21d3a.

It causes regressions for people using chips driven by the sungem
driver.  Suspicion is that the skb->csum value isn't being adjusted
properly.

The change also has a bug in that if __pskb_trim() fails, we'll leave
a corruped skb->csum value in there.  We would really need to revert
it to it's original value in that case.

Signed-off-by: David S. Miller <davem@davemloft.net>