bpf: Disable xfrm_decode_session hook attachment

In the Linux kernel, the following vulnerability has been resolved: bpf: Disable xfrm_decode_session hook attachment BPF LSM programs can currently attach to xfrm_decode_session(). That hook may return an error, but security_skb_classify_flow() calls it from a void path and triggers BUG_ON() if an error is returned. Disable BPF attachment to the hook to prevent a BPF LSM program from turning packet classification into a full panic.