selftests/bpf: Fix strict mode calculation

"(__LIBBPF_STRICT_LAST - 1) & ~LIBBPF_STRICT_MAP_DEFINITIONS" is wrong
as it is equal to 0 (LIBBPF_STRICT_NONE). Let's use
"LIBBPF_STRICT_ALL & ~LIBBPF_STRICT_MAP_DEFINITIONS" now that the
previous commit makes it possible in libbpf.

Fixes: 93b8952d ("libbpf: deprecate legacy BPF map definitions")
Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220207145052.124421-4-mauricio@kinvolk.io

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

@@ -4580,7 +4580,7 @@ static void do_test_file(unsigned int test_num)
 	btf_ext__free(btf_ext);
 
 	/* temporary disable LIBBPF_STRICT_MAP_DEFINITIONS to test legacy maps */
-	libbpf_set_strict_mode((__LIBBPF_STRICT_LAST - 1) & ~LIBBPF_STRICT_MAP_DEFINITIONS);
+	libbpf_set_strict_mode(LIBBPF_STRICT_ALL & ~LIBBPF_STRICT_MAP_DEFINITIONS);
 	obj = bpf_object__open(test->file);
 	err = libbpf_get_error(obj);
 	if (CHECK(err, "obj: %d", err))