net.websocket: fix server not listening for IPv4 (#12717)

vlib/net/udp_test.v

@@ -15,21 +15,20 @@ fn echo_server(mut c net.UdpConn) {
 }
 
 const (
-	local_addr  = ':40003'
-	remote_addr = 'localhost:40003'
+	server_addr = '127.0.0.1:40003'
 )
 
 fn echo() ? {
-	mut c := net.dial_udp(remote_addr) ?
+	mut c := net.dial_udp(server_addr) or { panic('could not net.dial_udp: $err') }
 	defer {
 		c.close() or {}
 	}
 	data := 'Hello from vlib/net!'
 
-	c.write_string(data) ?
+	c.write_string(data) or { panic('could not write_string: $err') }
 
 	mut buf := []byte{len: 100, init: 0}
-	read, addr := c.read(mut buf) ?
+	read, addr := c.read(mut buf) or { panic('could not read: $err') }
 
 	assert read == data.len
 	println('Got address $addr')
@@ -47,17 +46,10 @@ fn echo() ? {
 }
 
 fn test_udp() {
-	mut l := net.listen_udp(local_addr) or {
-		println(err)
-		assert false
-		panic('')
-	}
+	mut l := net.listen_udp(server_addr) or { panic('could not listen_udp: $err') }
 
 	go echo_server(mut l)
-	echo() or {
-		println(err)
-		assert false
-	}
+	echo() or { panic('could not echo: $err') }
 
 	l.close() or {}
 }