Merge branch 'Avoid dummy bpf_offload_netdev in __bpf_prog_dev_bound_init'

Eduard Zingerman says:

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For a device bound BPF program with flag BPF_F_XDP_DEV_BOUND_ONLY,
in case if device does not support offload, __bpf_prog_dev_bound_init()
creates a dummy bpf_offload_netdev struct with .offdev field set to NULL.

This dummy struct might be reused for programs without this flag
bound to the same device. However, bpf_prog_offload_verifier_prep()
that uses bpf_offload_netdev assumes that .offdev field cannot be NULL.

This bug was reported by syzbot in [1].

[1] https://lore.kernel.org/bpf/000000000000d97f3c060479c4f8@google.com/
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Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>