Simple Fix: Sort Ingress Servers to ensure default is first

[azweb76]

The sort logic is sorting alphabetically which places the default ("_") between servers that start with numbers and servers that start with characters. This is causing the first numeric server to be returned if no servers match SNI.

https://github.com/kubernetes/ingress/blob/master/core/pkg/ingress/sort_ingress.go#L57

Add the following:

  if c[j].Name == "_" {
    return false
  }
  return c[i].Name < c[j].Name