Merge branch 'bpf: Fix src IP addr related limitation in bpf_*_fib_lookup()'

Martynas Pumputis says:

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The patchset fixes the limitation of bpf_*_fib_lookup() helper, which
prevents it from being used in BPF dataplanes with network interfaces
which have more than one IP addr. See the first patch for more details.
Thanks!

* v2->v3: Address Martin KaFai Lau's feedback
* v1->v2: Use IPv6 stubs to fix compilation when CONFIG_IPV6=m.
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Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>