change import from packet_in to controller

src/openflow/controller.rs

 use std::{collections::HashMap, io::Write, mem::size_of, net::TcpStream};
 
-use super::{events::packet_in::PacketInEvent, OfpHeader};
+use super::{events::PacketInEvent, OfpHeader};
 
 pub struct Controller {
     version: u8,

src/openflow/events/mod.rs

 pub mod packet_in;
+pub use packet_in::{PacketInEvent, PacketInReason};