Revert "ip_gre: increase inner ip header ID during segmentation"

This reverts commit 10c0d7ed.
Next commit makes this commit unnecessary.

Acked-by: Cong Wang <amwang@redhat.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>