[SFlowMgr] Sflow Crash on 200G ports handled (#1683)

- What I did
Added 200G entry into the speed-rate map. Also handled the case which programs empty string into APP-DB and thus leading to a failure of Orchagent.
Default Sampling rate for 200G is set to 20000

- Why I did it
Fix for Issue: sonic-net/sonic-buildimage#6793

- How I verified it
run sflow community test under sonic-mgmt

Co-authored-by: Vivek Reddy Karri <vkarri@nvidia.com>

cfgmgr/sflowmgr.cpp

@@ -13,6 +13,7 @@ using namespace swss;
 map<string,string> sflowSpeedRateInitMap =
 {
     {SFLOW_SAMPLE_RATE_KEY_400G, SFLOW_SAMPLE_RATE_VALUE_400G},
+    {SFLOW_SAMPLE_RATE_KEY_200G, SFLOW_SAMPLE_RATE_VALUE_200G},
     {SFLOW_SAMPLE_RATE_KEY_100G, SFLOW_SAMPLE_RATE_VALUE_100G},
     {SFLOW_SAMPLE_RATE_KEY_50G, SFLOW_SAMPLE_RATE_VALUE_50G},
     {SFLOW_SAMPLE_RATE_KEY_40G, SFLOW_SAMPLE_RATE_VALUE_40G},
@@ -229,7 +230,7 @@ void SflowMgr::sflowCheckAndFillValues(string alias, vector<FieldValueTuple> &va
         {
             string speed = m_sflowPortConfMap[alias].speed;
 
-            if (speed != SFLOW_ERROR_SPEED_STR)
+            if (speed != SFLOW_ERROR_SPEED_STR && sflowSpeedRateInitMap.find(speed) != sflowSpeedRateInitMap.end())
             {
                 rate = sflowSpeedRateInitMap[speed];
             }

cfgmgr/sflowmgr.h

@@ -11,6 +11,7 @@
 namespace swss {
 
 #define SFLOW_SAMPLE_RATE_KEY_400G "400000"
+#define SFLOW_SAMPLE_RATE_KEY_200G "200000"
 #define SFLOW_SAMPLE_RATE_KEY_100G "100000"
 #define SFLOW_SAMPLE_RATE_KEY_50G  "50000"
 #define SFLOW_SAMPLE_RATE_KEY_40G  "40000"
@@ -19,6 +20,7 @@ namespace swss {
 #define SFLOW_SAMPLE_RATE_KEY_1G   "1000"
 
 #define SFLOW_SAMPLE_RATE_VALUE_400G "40000"
+#define SFLOW_SAMPLE_RATE_VALUE_200G "20000"
 #define SFLOW_SAMPLE_RATE_VALUE_100G "10000"
 #define SFLOW_SAMPLE_RATE_VALUE_50G  "5000"
 #define SFLOW_SAMPLE_RATE_VALUE_40G  "4000"