selftests: forwarding: lib: Add ping6_, ping_test_fails()

Add two helpers to run a ping test that succeeds when the pings themselves
fail.

Signed-off-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: Danielle Ratson <danieller@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -1215,6 +1215,15 @@ ping_test()
 	log_test "ping$3"
 }
 
+ping_test_fails()
+{
+	RET=0
+
+	ping_do $1 $2
+	check_fail $?
+	log_test "ping fails$3"
+}
+
 ping6_do()
 {
 	local if_name=$1
@@ -1237,6 +1246,15 @@ ping6_test()
 	log_test "ping6$3"
 }
 
+ping6_test_fails()
+{
+	RET=0
+
+	ping6_do $1 $2
+	check_fail $?
+	log_test "ping6 fails$3"
+}
+
 learning_test()
 {
 	local bridge=$1