Freedom: Fix UDP reply mismatch-address

[patterniha]

the problem:

the problem #4800 (comment) is because after browser sending UDP-data(quic initial packet) the packet correctly reaches to the final-target but the response-data does not reach to the browser, this problem happen when target-address is domain, let's explain why:

code-A (freedom.go > ReadMultiBuffer):

Xray-core/proxy/freedom/freedom.go

Lines 309 to 313 in fbae89d

	b.UDP = &net.Destination{
	Address: net.IPAddress(d.(*net.UDPAddr).IP),
	Port: net.Port(d.(*net.UDPAddr).Port),
	Network: net.Network_UDP,
	}

code-B (udp/dispatcher.go > handleInput):

Xray-core/transport/internet/udp/dispatcher.go

Lines 135 to 138 in fbae89d

	callback(ctx, &udp.Packet{
	Payload: b,
	Source: dest,
	})

code-C (socks/server.go):

Xray-core/proxy/socks/server.go

Lines 237 to 243 in fbae89d

	if payload.UDP != nil {
	request = &protocol.RequestHeader{
	User: request.User,
	Address: payload.UDP.Address,
	Port: payload.UDP.Port,
	}
	}

suppose browser send UDP-socks-request(UDP-associate) and target is cloudflare-quic.com:443.

each request packet consists of header+payload and header is "cloudflare-quic:443".

the response packet is also consists header+payload, the response-header must also be "cloudflare-quic.com", otherwise browser does not accept the received data.

to sending packet to "cloudflare-quic.com", Xray-core must resolve it to IP, suppose resolved-IP is "188.114.98.0".
after sending data, ReadMultiBuffer function receive response-data and because packet received from "188.114.98.0", it set b.UDP(buffer-UDP) address to "188.114.98.0" ---> code-A

after udp-dispatcher call a "callback" and pass the buffer(b) to that ---> code-B

if for example inbound is socks-protocol the 'callback" is "udpServer" in "socks/server.go > handleUDPPayload".

because payload.UDP is not nil and is equal to "188.114.98.0:443", the response-header-address overridden by "188.114.98.0:443", but the request-header was "cloudflare-quic.com" so the browser reject the response. ---> code-C

In short:

in short, the request and response header must be same but if address is domain(or fakedns) Xray-core send resolved-IP as a response header and this causes the browser to reject the packet.

so if the address is domain or fakedns or changed by redirect settings, Xray-core should ignore response-IP-address and send request-header-address as a response-header-address.

[RPRX]

这一天天的代码改得我都不认识了，先合了，新版有问题的话就找你们