bgpd: fix addressing information of non established outgoing sessions

bgpd: fix addressing information of non established outgoing sessions

When trying to connect to a BGP peer that does not respons, the 'show
bgp neighbors' command does not give any indication on the local and
remote addresses used:

> # show bgp neighbors
>  BGP neighbor is 192.0.2.150, remote AS 65500, local AS 65500, internal link
>   Local Role: undefined
>   Remote Role: undefined
>   BGP version 4, remote router ID 0.0.0.0, local router ID 192.0.2.1
>   BGP state = Connect
> [..]
>   Connections established 0; dropped 0
>   Last reset 00:00:04,   Waiting for peer OPEN (n/a)
>   Internal BGP neighbor may be up to 255 hops away.
> BGP Connect Retry Timer in Seconds: 120
> Next connect timer due in 117 seconds
> Read thread: off  Write thread: off  FD used: 27

The addressing information (address and port) are only available
when TCP session is established, whereas this information is present
at the system level:

> root@ubuntu2204:~# netstat -pan | grep 192.0.2.1
> tcp        0      0 192.0.2.1:179           192.0.2.150:38060       SYN_RECV    -
> tcp        0      1 192.0.2.1:46526         192.0.2.150:179         SYN_SENT    488310/bgpd

Add the display for outgoing BGP session, as the information in
the getsockname() API provides information for connected streams.
When getpeername() API does not give any information, use the peer
configuration (destination port is encoded in peer->port).

> # show bgp neighbors
> BGP neighbor is 192.0.2.150, remote AS 65500, local AS 65500, internal link
>   Local Role: undefined
>   Remote Role: undefined
>   BGP version 4, remote router ID 0.0.0.0, local router ID 192.0.2.1
>   BGP state = Connect
> [..]
>   Connections established 0; dropped 0
>   Last reset 00:00:16,   Waiting for peer OPEN (n/a)
> Local host: 192.0.2.1, Local port: 46084
> Foreign host: 192.0.2.150, Foreign port: 179

Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>