ip-header id needs to be incremented even if IP_DF flag is set.
This behaviour was changed in commit 490ab08127cebc25e3a26
(IP_GRE: Fix IP-Identification).
Following patch fixes it so that identification is always
incremented.
Reported-by: Cong Wang <amwang@redhat.com> Acked-by: Cong Wang <amwang@redhat.com> Signed-off-by: Pravin B Shelar <pshelar@nicira.com>