Return object icluding stat id for selected pair

Returning the object with stat id is useful when cross-referencing
stats.

icetransport.go

@@ -67,7 +67,7 @@ func (t *ICETransport) GetSelectedCandidatePair() (*ICECandidatePair, error) {
  return nil, err
  }
 
- return &ICECandidatePair{Local: &local, Remote: &remote}, nil
+ return NewICECandidatePair(&local, &remote), nil
 }
 
 // NewICETransport creates a new NewICETransport.