[Dell] S6100 - Update EEPROM API serial_number_str to return service tag instead of serial number (sonic-net#17440)

To modify EEPROM API serial_number_str to return service tag instead of serial number in Dell S6100.
Ref PR: sonic-net#1239

How I did it
Update EEPROM API serial_number_str to return service tag instead of serial number.

How to verify it
Verify decode-syseeprom -s returns service tag in Dell S6100.

Author: ArunSaravananBalachandran

platform/broadcom/sonic-platform-modules-dell/s6100/sonic_platform/chassis.py

@@ -207,7 +207,7 @@ def get_serial(self):
         Returns:
             string: Serial number of chassis
         """
-        return self._eeprom.serial_str()
+        return self._eeprom.serial_number_str()
 
     def get_status(self):
         """

platform/broadcom/sonic-platform-modules-dell/s6100/sonic_platform/eeprom.py

@@ -78,8 +78,14 @@ def __init__(self, i2c_line=0, iom_eeprom=False):
                 self.eeprom_tlv_dict[mac_code] = '00:00:00:00:00:00'
 
     def serial_number_str(self):
-        (is_valid, results) = self.get_tlv_field(
-                    self.eeprom_data, self._TLV_CODE_SERIAL_NUMBER)
+        # For Chassis, return service tag instead of serial number
+        if not self.is_module:
+            (is_valid, results) = self.get_tlv_field(
+                        self.eeprom_data, self._TLV_CODE_SERVICE_TAG)
+        else:
+            (is_valid, results) = self.get_tlv_field(
+                        self.eeprom_data, self._TLV_CODE_SERIAL_NUMBER)
+
         if not is_valid:
             return "N/A"
 
@@ -113,14 +119,6 @@ def part_number_str(self):
 
         return results[2].decode('ascii')
 
-    def serial_str(self):
-        (is_valid, results) = self.get_tlv_field(
-                    self.eeprom_data, self._TLV_CODE_SERVICE_TAG)
-        if not is_valid:
-            return "N/A"
-
-        return results[2].decode('ascii')
-
     def revision_str(self):
         (is_valid, results) = self.get_tlv_field(
                     self.eeprom_data, self._TLV_CODE_LABEL_REVISION)

platform/broadcom/sonic-platform-modules-dell/s6100/sonic_platform/module.py

@@ -139,7 +139,7 @@ def get_serial(self):
         Returns:
             string: Serial number of module
         """
-        return self._eeprom.serial_str()
+        return self._eeprom.serial_number_str()
 
     def get_status(self):
         """