net.socket: windows fixes and test

* added missing ai_canonname in addrinfo structure
* ai_canonname, ai_addr and ai_addrlen must be zeroed before getaddrinfo call
* write() must not be used on windows sockets
* added (Socket).get_port() function which is useful when socket was initialized with 0 (random) port
* tests is fixed, test server started listening on random port to avoid conflicts

vlib/net/socket_test.v

@@ -1,30 +1,29 @@
 import net 
 
 fn test_socket() {
-//	server := net.listen(8080) or {
-//		println(err)
-//		return
-//	}
-//	println(server)
-//	client := net.dial('127.0.0.1', 8080) or {
-//		println(err)
-//		return
-//	}
-//	println(client)
-//	socket := server.accept() or {
-//		println(err)
-//		return
-//	}
-//	println(socket)
-//
-//	message := 'Hello World'
-//	socket.send(message.str, message.len)
-//	println('Sent: ' + message)
-//
-//	bytes := client.recv(1024)
-//	println('Received: ' + tos(bytes, message.len))
-//
-//	server.close()
-//	client.close()
-//	socket.close()
+	mut server := net.listen(0) or {
+		println(err)
+		return
+	}    
+	server_port := server.get_port()
+	mut client := net.dial('127.0.0.1', server_port) or {
+		println(err)
+		return
+	}
+	mut socket := server.accept() or {
+		println(err)
+		return
+	}
+	
+	message := 'Hello World'
+	socket.send(message.str, message.len)	
+
+	bytes := client.recv(1024)
+	received := tos(bytes, message.len)
+
+	assert message == received
+
+	server.close()
+	client.close()
+	socket.close()
 }