bgpd: Show neighbors software version if description is not set

bgpd: Show neighbors software version if description is not set

Also, this is visible only if `capability software-version` is enabled.

Example:

```
r1# show ip bgp summary

IPv4 Unicast Summary (VRF default):
BGP router identifier 192.168.1.1, local AS number 65001 vrf-id 0
BGP table version 0
RIB entries 0, using 0 bytes of memory
Peers 1, using 725 KiB of memory

Neighbor        V         AS   MsgRcvd   MsgSent   TblVer  InQ OutQ  Up/Down State/PfxRcd   PfxSnt Desc
192.168.1.2     4      65002        54        54        0    0    0 00:00:52            0        0 FRRouting/9.1-dev-My

Total number of neighbors 1
r1#
```

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>