[atlas] No address in the results when ping or traceroute fail?

When a ping or traceroute emasurement fails, we do not know the IP
address of the probe (empty "from" and no "src_addr"), which is
annoying when you want to analyze the possible causes of the failure:

  {
    "size": 20, 
    "addr": "2620:0:2d0:200:0:0:0:7", 
    "min": -1, 
    "rcvd": 0, 
    "from": "", 
    "dst_name": "2620:0:2d0:200:0:0:0:7", 
    "af": 6, 
    "timestamp": 1374395985, 
    "fw": 4520, 
    "proto": "ICMP", 
    "name": "www.icann.org", 
    "prb_id": 3953, 
    "result": [
      {
        "error": "sendto failed: Network is unreachable"
      }, 
      {
        "error": "sendto failed: Network is unreachable"
      }, 
      {
        "error": "sendto failed: Network is unreachable"
      }
    ], 
    "max": -1, 
    "dup": 0, 
    "avg": -1, 
    "type": "ping", 
    "dst_addr": "2620:0:2d0:200::7", 
    "sent": 0, 
    "msm_id": 1013576
  },