core: add missing pcap file

Author: ignoramous

intra/core/pcap.go

@@ -0,0 +1,18 @@
+// Copyright (c) 2024 RethinkDNS and its authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package core
+
+// from: github.com/google/gvisor/blob/596e8d22/pkg/tcpip/link/sniffer/pcap.go#L26
+type PcapHeader struct {
+	MagicNumber  uint32
+	VersionMajor uint16
+	VersionMinor uint16
+	Thiszone     int32
+	Sigfigs      uint32
+	Snaplen      uint32
+	Network      uint32
+}