[PATCH bpf-next V1] selftests/bpf: Fix check_mtu using wrong variable type

[Jesper Dangaard Brouer <brouer@xxxxxxxxxx>]

Dan Carpenter found via Smatch static checker, that unsigned
'mtu_lo' is never less than zero.

Variable mtu_lo should have been an 'int', because read_mtu_device_lo()
uses minus as error indications.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/check_mtu.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/check_mtu.c b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
index 5338d2ea0460..2a9a30650350 100644
--- a/tools/testing/selftests/bpf/prog_tests/check_mtu.c
+++ b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
@@ -183,7 +183,7 @@ static void test_check_mtu_tc(__u32 mtu, __u32 ifindex)
 
 void serial_test_check_mtu(void)
 {
-	__u32 mtu_lo;
+	int mtu_lo;
 
 	if (test__start_subtest("bpf_check_mtu XDP-attach"))
 		test_check_mtu_xdp_attach();