[chassis] Fixed bug in Fabric monitor capacity (#4057)

What I did
sonic-net/sonic-buildimage#24828
Fixed a bug in updateFabricCapacity for fabric monitor feature . Without this fix, the show fabric monitor shows wrong operating links and also raises the false alarm in the syslog which could trigger the monitoring tool to isolate the chassis in the production. In the below output, only 1 port was isolated out of 24 ports, however the operating links shows only 5.
image

Why I did it
When the fabric port sees CRC/FEC-Uncorrectable error, the Fabric monitor feature Isolates the port and sets the ISOALTED=1 and also AUTO_ISOLATED=1 in the STATE_DB for that port in the FABRIC_PORT_TABLE. The field ISOLATED and CONFIG_ISOLATED are always present for all the fabric ports in FABRIC_PORT_TABLE. However the field AUTO_ISOLATED is not present always and added only when the port is auto ISOLATED.
So due to the bug in the updateFabricCapacity function, the operating_links is calculated wrong, and the syslog is printed even if 1 link is isolated and didn't reach the threshold.

Author: saksarav-nokia

orchagent/fabricportsorch.cpp

@@ -1047,10 +1047,6 @@ void FabricPortsOrch::updateFabricCapacity()
     // Init value for fabric capacity monitoring
     int capacity = 0;
     int downCapacity = 0;
-    string lnkStatus = "down";
-    string configIsolated = "0";
-    string isolated = "0";
-    string autoIsolated = "0";
     int operating_links = 0;
     int total_links = 0;
     int threshold = 100;
@@ -1088,6 +1084,10 @@ void FabricPortsOrch::updateFabricCapacity()
         string key = FABRIC_PORT_PREFIX + to_string(lane);
         std::vector<FieldValueTuple> values;
         string valuePt;
+        string lnkStatus = "down";
+        string configIsolated = "0";
+        string isolated = "0";
+        string autoIsolated = "0";
 
         // Get fabric serdes link status from STATE_DB
         bool exist = m_stateTable->get(key, values);