selftests/bpf: Don't assume page size is 4096

The verifier test creates BPF ringbuf maps using hard-coded
4096 as max_entries. Some tests will fail if the page size
of the running kernel is not 4096. Use getpagesize() instead.
Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230326095341.816023-1-hengqi.chen@gmail.com

tools/testing/selftests/bpf/test_verifier.c

@@ -1079,7 +1079,7 @@ static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
 	}
 	if (*fixup_map_ringbuf) {
 		map_fds[20] = create_map(BPF_MAP_TYPE_RINGBUF, 0,
-					   0, 4096);
+					 0, getpagesize());
 		do {
 			prog[*fixup_map_ringbuf].imm = map_fds[20];
 			fixup_map_ringbuf++;