Add namespace support for show interface neighbor expected (#3781)

What I did
Adding namespace support for show interface neighbor expected. So that we can use

show interface neighbor expected -n asic0
How I did it
How to verify it
Verified on T2 testbed

Previous command output (if the output of a command-line utility has changed)
admin@somehost:/var/log$ show interfaces neighbor expected -n asic1
Usage: show interfaces neighbor expected [OPTIONS] [INTERFACENAME]
Try "show interfaces neighbor expected -h" for help.

Error: no such option: -n
New command output (if the output of a command-line utility has changed)
admin@somehost:/var/log$ show interfaces neighbor expected -n asic1
LocalPort    Neighbor    NeighborPort    NeighborLoopback    NeighborMgmt    NeighborType
-----------  ----------  --------------  ------------------  --------------  --------------
Ethernet96   ARISTAXXTX  Ethernet1       None                XXX.XX.XXX.XX   someHub
Ethernet104  ARISTAXXTX Ethernet1       None                XXX.XX.XXX.XX   otherHub
...

Signed-off-by: Austin Pham <[email protected]>

Author: auspham

doc/Command-Reference.md

@@ -5447,7 +5447,7 @@ This command is used to display the list of expected neighbors for all interface
 
 - Usage:
   ```
-  show interfaces neighbor expected [<interface_name>]
+  show interfaces neighbor expected [<interface_name>] -n [<namespace>]
   ```
 
 - Example:

show/interfaces/__init__.py

@@ -297,16 +297,20 @@ def neighbor():
 # 'expected' subcommand ("show interface neighbor expected")
 @neighbor.command()
 @click.argument('interfacename', required=False)
+@multi_asic_util.multi_asic_click_option_namespace
 @clicommon.pass_db
-def expected(db, interfacename):
+def expected(db, interfacename, namespace):
     """Show expected neighbor information by interfaces"""
 
-    neighbor_dict = db.cfgdb.get_table("DEVICE_NEIGHBOR")
+    if not namespace:
+        namespace = multi_asic_util.constants.DEFAULT_NAMESPACE
+
+    neighbor_dict = db.cfgdb_clients[namespace].get_table("DEVICE_NEIGHBOR")
     if neighbor_dict is None:
         click.echo("DEVICE_NEIGHBOR information is not present.")
         return
 
-    neighbor_metadata_dict = db.cfgdb.get_table("DEVICE_NEIGHBOR_METADATA")
+    neighbor_metadata_dict = db.cfgdb_clients[namespace].get_table("DEVICE_NEIGHBOR_METADATA")
     if neighbor_metadata_dict is None:
         click.echo("DEVICE_NEIGHBOR_METADATA information is not present.")
         return