add remote_system_mgmt_ip key to lldp dict

[ratneshnagori]

get_lldp_neighbors_detail() returns dictionary of all the lldp neighbors on a switch. However, it doesn't have remote system's management ip. This will come in handy when you are building a network topology.

We already receive the remote system's mgmt ip from _lldp_detail_parser(), so this pull request is to just add a key value pair for mgmt ip.