veristat: change guess for __sk_buff from CGROUP_SKB to SCHED_CLS

SCHED_CLS seems to be a better option as a default guess for freplace
programs that have __sk_buff as a context type.

Reported-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230330190115.3942962-1-andrii@kernel.org


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>