Merge branch 'fix-bpf_strnstr-len-error'

Rong Tao says:

====================
Fix bpf_strnstr() wrong 'len' parameter, bpf_strnstr("open", "open", 4)
should return 0 instead of -ENOENT. And fix a more general case when s2
is a suffix of the first len characters of s1.
====================

Link: https://patch.msgid.link/tencent_E72A37AF03A3B18853066E421B5969976208@qq.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>