skbuff: skb_segment: orphan frags before copying

skbuff: skb_segment: orphan frags before copying

skb_segment copies frags around, so we need
to copy them carefully to avoid accessing
user memory after reporting completion to userspace
through a callback.

skb_segment doesn't normally happen on datapath:
TSO needs to be disabled - so disabling zero copy
in this case does not look like a big deal.

Signed-off-by: Michael S. Tsirkin <[email protected]>
Acked-by: Herbert Xu <[email protected]>
Signed-off-by: David S. Miller <[email protected]>