bgpd: List peer-group as neighbor once and not for IPv4/IPv6/WORD

bgpd: List peer-group as neighbor once and not for IPv4/IPv6/WORD

Before:

```
exit1-debian-11(config-router)# neighbor ?
  A.B.C.D   Neighbor address
     192.168.0.2 PEER PG
  WORD      Interface name or neighbor tag
     PEER PG
  X:X::X:X  Neighbor IPv6 address
     2a02:abc::17 2a02:bbd::2 PEER PG
```

After:

```
exit1-debian-11(config-router)# neighbor ?
  A.B.C.D   Neighbor address
     192.168.0.2
  WORD      Interface name or neighbor tag
     PEER PG
  X:X::X:X  Neighbor IPv6 address
     2a02:abc::17 2a02:bbd::2
```

Signed-off-by: Donatas Abraitis <donatas.abraitis@gmail.com>