1. avoid dns query hangs the thread
2. avoid deadloop when stun query failed because of no ipv4 addr.
3. make quic input error non-fatal.
4. remove ring tunnel from connection map to avoid mem leak.
5. limit listener retry count.
Some devices have ipv6 but don't allow input connection, this patch add hole punching for these devices.
- **add v6 hole punch msg to udp tunnel**
- **send hole punch packet when do ipv6 direct connect**
this patch optimize the udp hole punch logic:
1. allow start punch hole before stun test complete.
2. add lock to symmetric punch, avoid conflict between concurrent hole punching task.
3. support punching hole for predictable nat4-nat4.
4. make backoff of retry reasonable
KKRainbow