junos: make sure we don't duplicate lldp neighbor entries

[matejv]

if an interface had 3 LLDP neighbors function returned 3*3=9 entries - each was returned 3 times

Example from one of our switches:

matej@myswitch> show lldp neighbors | match 0/0/16    
ge-0/0/16          -                   54:bf:64:94:4d:9e   54:bf:64:94:4d:9e
ge-0/0/16          -                   7c:8a:e1:76:d3:f7   7c:8a:e1:76:d3:f7

Note two LLDP neighbors on the same interface.

$ napalm --user matej --vendor junos myswitch call get_lldp_neighbors_detail
Enter password: 
{
...
    "ge-0/0/16": [
        {
            "parent_interface": "-",
            "remote_port": "54:bf:64:94:4d:9e",
            "remote_chassis_id": "54:BF:64:94:4D:9E",
            "remote_port_description": "",
            "remote_system_name": null,
            "remote_system_description": null,
            "remote_system_capab": [],
            "remote_system_enable_capab": []
        },
        {
            "parent_interface": "-",
            "remote_port": "7c:8a:e1:76:d3:f7",
            "remote_chassis_id": "7C:8A:E1:76:D3:F7",
            "remote_port_description": "",
            "remote_system_name": null,
            "remote_system_description": null,
            "remote_system_capab": [],
            "remote_system_enable_capab": []
        },
        {
            "parent_interface": "-",
            "remote_port": "54:bf:64:94:4d:9e",
            "remote_chassis_id": "54:BF:64:94:4D:9E",
            "remote_port_description": "",
            "remote_system_name": null,
            "remote_system_description": null,
            "remote_system_capab": [],
            "remote_system_enable_capab": []
        },
        {
            "parent_interface": "-",
            "remote_port": "7c:8a:e1:76:d3:f7",
            "remote_chassis_id": "7C:8A:E1:76:D3:F7",
            "remote_port_description": "",
            "remote_system_name": null,
            "remote_system_description": null,
            "remote_system_capab": [],
            "remote_system_enable_capab": []
        }
    ]
}

Note that each LLDP neighbor entry war returned twice. This pull request fixes that.