We can just use skb_shinfo(skb)->tso_{segs,size}
directly.  This also allows us to kill the
hack zone code in ip_output.c

The original impetus for thus change was a problem
noted by John Heffner.  We do not abide by the MSS
of the connection for TCP segmentation, we were using
the path MTU instead.  This broke various local
network setups with TSO enabled and is fixed as a side
effect of these changes.
Signed-off-by: David S. Miller <davem@davemloft.net>