[ycable][credo] Fix the is_link_active API for Credo Ycable (#260)

Signed-off-by: vaibhav-dahiya vdahiya@microsoft.com

Description
Currently is_link_active API was broken because it was not using the target param in the routine to give back the correct link_status of ecah side. With this change it gives the correct result.

Motivation and Context
Required for MUX_CABLE_INFO table in streaming telemetry if the cable is disconnected or the link is down.

redis-cli -n 6 hgetall "MUX_CABLE_INFO|Ethernet16"
"
 9) "link_status_self"
10) "down"
11) "link_status_peer"
12) "up"
13) "link_status_nic"
14) "up"
How Has This Been Tested?
Tested on actual Arista7050cx3 testbed.

sonic_y_cable/credo/y_cable_credo.py

@@ -787,15 +787,24 @@ def is_link_active(self, target):
 
         regval_read = struct.unpack(">B", result)
 
-        if (regval_read[0] & 0x01):
-            self.log_info("NIC link is up")
-            return True
-        elif ((regval_read[0] >> 2) & 0x01):
-            self.log_info("TOR A link is up")
-            return True
-        elif ((regval_read[0] >> 1) & 0x01):
-            self.log_info("TOR B link is up")
-            return True
+        if target == YCableBase.TARGET_NIC:
+            if (regval_read[0] & 0x01):
+                self.log_info("NIC link is up")
+                return True
+            else:
+                return False
+        elif target == YCableBase.TARGET_TOR_A:
+            if ((regval_read[0] >> 2) & 0x01):
+                self.log_info("TOR A link is up")
+                return True
+            else:
+                return False
+        elif target == YCableBase.TARGET_TOR_B:
+            if ((regval_read[0] >> 1) & 0x01):
+                self.log_info("TOR B link is up")
+                return True
+            else:
+                return False
         else:
             return YCableBase.TARGET_UNKNOWN