Fix dumping OVS flows of a NetworkPolicy

Fixes #3306.

This commit adds test to verify the changes made to solve the nil pointer dereference error while dumping ovsflows of NetworkPolicy.

Signed-off-by: Pulkit Jain <jainpu@vmware.com>

pkg/agent/openflow/network_policy.go

@@ -525,7 +525,8 @@ type policyRuleConjunction struct {
 	serviceClause *clause
 	actionFlows   []binding.Flow
 	metricFlows   []binding.Flow
-	// NetworkPolicy reference information for debugging usage.
+	// NetworkPolicy reference information for debugging usage, its' value can be nil
+	// when a new DNS Conjunction is added to the policyCache.
 	npRef       *v1beta2.NetworkPolicyReference
 	ruleTableID uint8
 }

pkg/agent/openflow/network_policy_test.go

@@ -222,6 +222,10 @@ func TestInstallPolicyRuleFlows(t *testing.T) {
 	assert.Equal(t, 3, getChangedFlowOPCount(matchFlows2, insertion))
 	err = c.applyConjunctiveMatchFlows(ctxChanges2)
 	require.Nil(t, err)
+	// dnsID will store the ID for New DNS packet, that is created,
+	// to test for nil NetworkPolicyReference.
+	dnsID := uint32(107)
+	c.NewDNSpacketInConjunction(dnsID)
 
 	assert.Equal(t, 0, len(c.GetNetworkPolicyFlowKeys("np1", "ns1")))
 	err = c.InstallPolicyRuleFlows(rule2)