xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete

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Code injection

The pingunhash function in net/ipv4/ping.c in the Linux kernel before 4.0.3 does not initialize a certain list data structure during an unhash operation, which allows local users to gain privileges or cause a denial of service use-after-free and system crash by leveraging the ability to make a...