selftests/bpf: Fix bpf_cookie and find_vma in nested VM

bpf_cookie and find_vma are flaky in nested VMs, which is used by some CI
systems. It turns out these failures are caused by unreliable perf event
in nested VM. Fix these by:

1. Use PERF_COUNT_SW_CPU_CLOCK in find_vma;
2. Increase sample_freq in bpf_cookie.

Signed-off-by: Song Liu <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/testing/selftests/bpf/prog_tests/bpf_cookie.c

···
 	attr.type = PERF_TYPE_SOFTWARE;
 	attr.config = PERF_COUNT_SW_CPU_CLOCK;
 	attr.freq = 1;
-	attr.sample_freq = 1000;
+	attr.sample_freq = 10000;
 	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
 	if (!ASSERT_GE(pfd, 0, "perf_fd"))
 		goto cleanup;

tools/testing/selftests/bpf/prog_tests/find_vma.c

···
 
 	/* create perf event */
 	attr.size = sizeof(attr);
-	attr.type = PERF_TYPE_HARDWARE;
-	attr.config = PERF_COUNT_HW_CPU_CYCLES;
+	attr.type = PERF_TYPE_SOFTWARE;
+	attr.config = PERF_COUNT_SW_CPU_CLOCK;
 	attr.freq = 1;
 	attr.sample_freq = 1000;
 	pfd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, PERF_FLAG_FD_CLOEXEC);