ping: always initialize ->sin6_scope_id and ->sin6_flowinfo

If we don't need scope id, we should initialize it to zero.
Same for ->sin6_flowinfo.

Cc: Lorenzo Colitti <lorenzo@google.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Acked-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>