bgpd: totalPrefixCounter incorectly shows sent prefix count

bgpd: totalPrefixCounter incorectly shows sent prefix count

Using: show bgp ipv4 unicast neighbors 192.168.12.2 advertised-routes json

Before:

```
  "bgpOriginatingDefaultNetwork":"0.0.0.0\/0",
  "advertisedRoutes":{
    "192.168.12.0\/24":{
      "addrPrefix":"192.168.12.0",
      "prefixLen":24,
      "network":"192.168.12.0\/24",
      "nextHop":"0.0.0.0",
      "metric":0,
      "weight":32768,
      "path":"",
      "bgpOriginCode":"?",
      "appliedStatusSymbols":{
        "*":true,
        ">":true
      }
    }
  },
  "totalPrefixCounter":1,
  "filteredPrefixCounter":0
```

After:

```
  "bgpOriginatingDefaultNetwork":"0.0.0.0\/0",
  "advertisedRoutes":{
    "192.168.12.0\/24":{
      "addrPrefix":"192.168.12.0",
      "prefixLen":24,
      "network":"192.168.12.0\/24",
      "nextHop":"0.0.0.0",
      "metric":0,
      "weight":32768,
      "path":"",
      "bgpOriginCode":"?",
      "appliedStatusSymbols":{
        "*":true,
        ">":true
      }
    }
  },
  "totalPrefixCounter":2,
  "filteredPrefixCounter":0
```

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