[pfcwdorch]: Add alert mode (sonic-net#342)

Alert mode tells watchdog that whenever it detects PFC storm, it should
only write message to the log. It is implemented as a separate action
along with drop and forward.

Signed-off-by: marian-pritsak <marianp@mellanox.com>

orchagent/pfcactionhandler.h

@@ -21,7 +21,7 @@ class PfcWdActionHandler
     public:
         PfcWdActionHandler(sai_object_id_t port, sai_object_id_t queue,
                 uint8_t queueId, shared_ptr<Table> countersTable);
-        virtual ~PfcWdActionHandler(void) = 0;
+        virtual ~PfcWdActionHandler(void);
 
         inline sai_object_id_t getPort(void)
         {

orchagent/pfcwdorch.cpp

@@ -97,6 +97,7 @@ PfcWdAction PfcWdOrch<DropHandler, ForwardHandler>::deserializeAction(const stri
     {
         { "forward", PfcWdAction::PFC_WD_ACTION_FORWARD },
         { "drop", PfcWdAction::PFC_WD_ACTION_DROP },
+        { "alert", PfcWdAction::PFC_WD_ACTION_ALERT },
     };
 
     if (actionMap.find(key) == actionMap.end())
@@ -445,6 +446,14 @@ void PfcWdSwOrch<DropHandler, ForwardHandler>::handleWdNotification(swss::Notifi
                     entry->second.index,
                     PfcWdOrch<DropHandler, ForwardHandler>::getCountersTable());
         }
+        else if (entry->second.action == PfcWdAction::PFC_WD_ACTION_ALERT)
+        {
+            entry->second.handler = make_shared<PfcWdActionHandler>(
+                    entry->second.portId,
+                    entry->first,
+                    entry->second.index,
+                    PfcWdOrch<DropHandler, ForwardHandler>::getCountersTable());
+        }
         else
         {
             throw runtime_error("Unknown PFC WD action");

orchagent/pfcwdorch.h

@@ -18,6 +18,7 @@ enum class PfcWdAction
     PFC_WD_ACTION_UNKNOWN,
     PFC_WD_ACTION_FORWARD,
     PFC_WD_ACTION_DROP,
+    PFC_WD_ACTION_ALERT,
 };
 
 template <typename DropHandler, typename ForwardHandler>