Merge branch 'bpf: Allow helpers access ptr_to_btf_id.'

Alexei Starovoitov says:

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From: Alexei Starovoitov <ast@kernel.org>

Allow code like:
bpf_strncmp(task->comm, 16, "foo");
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Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>