Description: ip_gre: add validation for csum_start
References:
 https://source.android.com/security/bulletin/2022-01-01
Notes:
 carnil> Commit fixes c54419321455 ("GRE: Refactor GRE tunneling code.")
 carnil> in 3.10-rc1.
Bugs:
upstream: released (5.14) [1d011c4803c72f3907eccfc1ec63caefb852fcbf]
5.10-upstream-stable: released (5.10.62) [fb45459d9ddb1edd4a8b087bafe875707753cb10]
4.19-upstream-stable: released (4.19.206) [c33471daf2763c5aee2b7926202c74b75c365119]
4.9-upstream-stable: released (4.9.282) [41d5dfa408130433cc5f037ad89bed854bf936f7]
sid: released (5.14.6-1)
5.10-bullseye-security: released (5.10.70-1)
4.19-buster-security: released (4.19.208-1)
4.9-stretch-security: released (4.9.290-1)