Merge branch 'add-kfuncs-bpf_strcasestr-and-bpf_strncasestr'

Rong Tao says:

====================
Add kfuncs bpf_strcasestr and bpf_strncasestr

From: Rong Tao <rongtao@cestc.cn>

Add kfuncs bpf_strcasestr and bpf_strncasestr, which are extensions of
bpf_strstr and bpf_strnstr, suitable for more scenarios.

v4: Fix wrong comment.
v3: keep __bpf_strnstr() static and compress some tests.
    https://lore.kernel.org/lkml/tencent_6E59062E4249590597452A06AFCDA3098808@qq.com/
v2: remove extra __bpf_kfunc and fix comment of bpf_strncasestr().
    https://lore.kernel.org/all/tencent_6D228941AB904DD6E1E58C8ACDEBEC280C06@qq.com/
v1: https://lore.kernel.org/all/tencent_8AF4D15B4475031E2185ACDE4B1495995707@qq.com/
====================

Link: https://patch.msgid.link/tencent_98ABC9680EA2A20198904316DAE5A84AD906@qq.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>