This gives us the possibility to chose SS server based on dest address.

Now it will close all existing TCP relay connections
while reloading the listener.

Signed-off-by: noisyfox <timemanager.rick@gmail.com>

UDP SendTo doesn't support DnsEndPoint.

Signed-off-by: noisyfox <timemanager.rick@gmail.com>

-Use dual-mode socket & DnsEndPoint to handle all domain name connection.
-Move all socket creation into one single function.

So that we could treat domain name just like ipv4 & ipv6 address.
This also solves the async domain solving problem because the os will
hanlde it for us.

- use null conditional access in case some connections been
  cancelled unexpectedly and may cause null reference exception
- Refine error message
- use conditional operator to simplify some code

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

1/ removed dual empty line
2/ removed tailing spaces
3/ converted tabs into spaces
4/ added some TODO comments