fix show interface neighbor expected empty issue

[jcaiMR]

Why I did it

With the commit of sonic-net/sonic-buildimage#11894.
device neighbor metadata in config_db.json changed a little bit when "lo_addr"/"mgmt_addr" are None.

MSFT ADO: 15802924

CLI parse code for "show interface neighbor expected" is not strong enough to handle None case.
It always assume 'lo_addr' and 'mgmt_addr' exists, and will finally cause KeyError, show command will not print the information.

for port in natsorted(list(neighbor_dict.keys())):
            try:
                device = neighbor_dict[port]['name']
                body.append([port,
                             device,
                             neighbor_dict[port]['port'],
                             neighbor_metadata_dict[device]['lo_addr'],
                             neighbor_metadata_dict[device]['mgmt_addr'],
                             neighbor_metadata_dict[device]['type']])
            except KeyError:
                pass

How I did it

After discussion with team, we plan to keep current yang model change, but
add fields check for 'lo_addr', "mgmt_addr", "type"before access it.

How to verify it

"show interface neighbor expected" with fix image

fixes #12301

[StormLiangMS]

LGTM