[mirrororch]: Set the VLAN header only when the packet is mirrored to…

… a VLAN (sonic-net#282)

orchagent/mirrororch.cpp

@@ -396,25 +396,29 @@ bool MirrorOrch::activateSession(const string& name, MirrorEntry& session)
     attr.value.s32 = SAI_MIRROR_SESSION_TYPE_ENHANCED_REMOTE;
     attrs.push_back(attr);
 
-    attr.id = SAI_MIRROR_SESSION_ATTR_VLAN_HEADER_VALID;
-    attr.value.booldata = true;
-    attrs.push_back(attr);
+    /* Add the VLAN header when the packet is sent out from a VLAN */
+    if (session.neighborInfo.vlanId)
+    {
+        attr.id = SAI_MIRROR_SESSION_ATTR_VLAN_HEADER_VALID;
+        attr.value.booldata = true;
+        attrs.push_back(attr);
 
-    attr.id =SAI_MIRROR_SESSION_ATTR_VLAN_TPID;
-    attr.value.u16 = ETH_P_8021Q;
-    attrs.push_back(attr);
+        attr.id =SAI_MIRROR_SESSION_ATTR_VLAN_TPID;
+        attr.value.u16 = ETH_P_8021Q;
+        attrs.push_back(attr);
 
-    attr.id =SAI_MIRROR_SESSION_ATTR_VLAN_ID;
-    attr.value.u16 = session.neighborInfo.vlanId;
-    attrs.push_back(attr);
+        attr.id =SAI_MIRROR_SESSION_ATTR_VLAN_ID;
+        attr.value.u16 = session.neighborInfo.vlanId;
+        attrs.push_back(attr);
 
-    attr.id = SAI_MIRROR_SESSION_ATTR_VLAN_PRI;
-    attr.value.u8 = MIRROR_SESSION_DEFAULT_VLAN_PRI;
-    attrs.push_back(attr);
+        attr.id = SAI_MIRROR_SESSION_ATTR_VLAN_PRI;
+        attr.value.u8 = MIRROR_SESSION_DEFAULT_VLAN_PRI;
+        attrs.push_back(attr);
 
-    attr.id = SAI_MIRROR_SESSION_ATTR_VLAN_CFI;
-    attr.value.u8 = MIRROR_SESSION_DEFAULT_VLAN_CFI;
-    attrs.push_back(attr);
+        attr.id = SAI_MIRROR_SESSION_ATTR_VLAN_CFI;
+        attr.value.u8 = MIRROR_SESSION_DEFAULT_VLAN_CFI;
+        attrs.push_back(attr);
+    }
 
     attr.id = SAI_MIRROR_SESSION_ATTR_ERSPAN_ENCAPSULATION_TYPE;
     attr.value.s32 = SAI_ERSPAN_ENCAPSULATION_TYPE_MIRROR_L3_GRE_TUNNEL;