Fix backend port channels and routes being displayed

In `show interface portchannel` and `show ip route`, backend port
channels and routes were being displayed. This is due to changes in sonic-net#13660.
Fix these issues by switching to reading from PORTCHANNEL_MEMBERS table
instead.

Fixes sonic-net#14459.

Signed-off-by: Saikrishna Arcot <sarcot@microsoft.com>

src/sonic-py-common/sonic_py_common/multi_asic.py

@@ -354,13 +354,12 @@ def is_port_channel_internal(port_channel, namespace=None):
 
     for ns in ns_list:
         config_db = connect_config_db_for_ns(ns)
-        port_channels = config_db.get_entry(PORT_CHANNEL_CFG_DB_TABLE, port_channel)
+        port_channel_members = config_db.get_keys("PORTCHANNEL_MEMBER")
 
-        if port_channels:
-            if 'members' in port_channels:
-                members = port_channels['members']
-                if is_port_internal(members[0], namespace):
-                    return True
+        for port_channel_member in port_channel_members:
+            if port_channel_member[0] != port_channel:
+                continue
+            return is_port_internal(port_channel_member[1], namespace)
 
     return False
 
@@ -380,14 +379,14 @@ def get_back_end_interface_set(namespace=None):
         ns_list = get_namespace_list(namespace)
         for ns in ns_list:
             config_db = connect_config_db_for_ns(ns)
-            port_channels = config_db.get_table(PORT_CHANNEL_CFG_DB_TABLE)
+            port_channel_members = config_db.get_keys("PORTCHANNEL_MEMBER")
             # a back-end LAG must be configured with all of its member from back-end interfaces.
             # mixing back-end and front-end interfaces is miss configuration and not allowed.
             # To determine if a LAG is back-end LAG, just need to check its first member is back-end or not
             # is sufficient. Note that a user defined LAG may have empty members so the list expansion logic
             # need to ensure there are members before inspecting member[0].
-            bk_end_intf_list.extend([port_channel for port_channel, lag_info in port_channels.items()\
-                                if 'members' in lag_info and lag_info['members'][0] in bk_end_intf_list])
+            bk_end_intf_list.extend(set([port_channel_member[0] for port_channel_member in port_channel_members\
+                                if port_channel_member[1] in bk_end_intf_list]))
     a = set()
     a.update(bk_end_intf_list)
     return a