Implement is_copper for SFP

Author: Junchao-Mellanox

sonic_platform_base/sonic_xcvr/api/public/sff8472.py

@@ -295,3 +295,6 @@ def get_lpmode_support(self):
 
     def get_power_override_support(self):
         return False
+
+    def is_copper(self):
+        return self.xcvr_eeprom.read(consts.SFP_CABLE_TECH_FIELD) == 'Passive Cable'

tests/sonic_xcvr/test_sff8472.py

@@ -55,6 +55,7 @@ def test_api(self):
         self.api.get_transceiver_thresholds_support()
         self.api.get_lpmode_support()
         self.api.get_power_override_support()
+        self.api.is_copper()
 
     def test_temp(self):
         temp_field = self.mem_map.get_field(consts.TEMPERATURE_FIELD)