Socks4a server: Check if the client sends an IP address as domain (#3628)

Fixes https://github.com/XTLS/Xray-core/issues/3622

common/net/address.go

@@ -121,6 +121,11 @@ func IPAddress(ip []byte) Address {
 }
 
 // DomainAddress creates an Address with given domain.
+// This is an internal function that forcibly converts a string to domain.
+// It's mainly used in test files and mux.
+// Unless you have a specific reason, use net.ParseAddress instead,
+// as this function does not check whether the input is an IP address.
+// Otherwise, you will get strange results like domain: 1.1.1.1
 func DomainAddress(domain string) Address {
 	return domainAddress(domain)
 }