selftests: forwarding: bail_on_lldpad() should SKIP

$ksft_skip is used to mark selftests that have tooling issues. The fact
that LLDPad is running, but shouldn't, is one such issue. Therefore have
bail_on_lldpad() bail with $ksft_skip.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Benjamin Poirier <bpoirier@nvidia.com>
Reviewed-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

tools/testing/selftests/net/forwarding/lib.sh

@@ -2138,6 +2138,8 @@ bail_on_lldpad()
 {
 	local reason1="$1"; shift
 	local reason2="$1"; shift
+	local caller=${FUNCNAME[1]}
+	local src=${BASH_SOURCE[1]}
 
 	if systemctl is-active --quiet lldpad; then
 
@@ -2158,7 +2160,8 @@ bail_on_lldpad()
 				an environment variable ALLOW_LLDPAD to a
 				non-empty string.
 			EOF
-			exit 1
+			log_test_skip $src:$caller
+			exit $EXIT_STATUS
 		else
 			return
 		fi