Due to IP_GRE GSO support, GRE can recieve non linear skb which
results in panic in case of GRE_CSUM. Following patch fixes it by
using correct csum API.
Bug introduced in commit 6b78f16e4b (gre: add GSO support)
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>