bgpd: Adding BGP neighbor JSON output for neighbors never established a BGP adjacency

bgpd: Adding BGP neighbor JSON output for neighbors never established a BGP adjacency

Some keys are only present in the JSON data of BGP neighbors are only present if the peer is, or has previously been established.
While they are not present if the peer has never come up.

To keep the data structure aligned, the below keys are added also to the neighbors that BGP adjacency has never been established.
Values of the keys are all set to Unknown
    hostname:Unknown,
    nexthop:Unknown,
    nexthopGlobal:Unknown,
    nexthopLocal:Unknown,
    bgpConnection:Unknown,

Signed-off-by: Karl Quan <kquan@nvidia.com>