[route_check] fix IPv6 address handling (#2798)

BACKPORT of #2722

What I did
In case user has configured an IPv6 address on an interface in CONFIG DB in non simplified form like 2000:31:0:0::1/64 it is present in a simplified form in ASIC_DB. This leads to route_check failure since it just compares strings.

How I did it
Convert prefix string using ip_network().

How to verify it
UT replicates the issue.

scripts/route_check.py

@@ -46,6 +46,7 @@
 import signal
 import traceback
 
+from ipaddress import ip_network
 from swsscommon import swsscommon
 from utilities_common import chassis
 
@@ -141,7 +142,7 @@ def add_prefix(ip):
         ip = ip + PREFIX_SEPARATOR + "32"
     else:
         ip = ip + PREFIX_SEPARATOR + "128"
-    return ip
+    return str(ip_network(ip))
 
 
 def add_prefix_ifnot(ip):
@@ -150,7 +151,7 @@ def add_prefix_ifnot(ip):
     :param ip: IP to add prefix as string.
     :return ip with prefix
     """
-    return ip if ip.find(PREFIX_SEPARATOR) != -1 else add_prefix(ip)
+    return str(ip_network(ip)) if ip.find(PREFIX_SEPARATOR) != -1 else add_prefix(ip)
 
 
 def is_local(ip):

tests/route_check_test_data.py

@@ -359,5 +359,23 @@
                 }
             }
         }
-    }
+    },
+    "10": {
+        DESCR: "basic good one with IPv6 address",
+        ARGS: "route_check -m INFO -i 1000",
+        PRE: {
+            APPL_DB: {
+                ROUTE_TABLE: {
+                },
+                INTF_TABLE: {
+                    "PortChannel1013:2000:31:0:0::1/64": {},
+                }
+            },
+            ASIC_DB: {
+                RT_ENTRY_TABLE: {
+                    RT_ENTRY_KEY_PREFIX + "2000:31::1/128" + RT_ENTRY_KEY_SUFFIX: {},
+                }
+            }
+        }
+    },
 }