Move ebpf code to its own package to avoid crash issues in Android (#1033)

* Move ebpf code to its own package to avoid crash issues in Android

Older versions of android crashes because of the bytecode files
Even when they aren't loaded as it was our case

* move c file to own folder

* fix lint

client/internal/wgproxy/ebpf/loader.go

@@ -0,0 +1,84 @@
+//go:build linux && !android
+
+package ebpf
+
+import (
+	_ "embed"
+	"net"
+
+	"github.com/cilium/ebpf/link"
+	"github.com/cilium/ebpf/rlimit"
+)
+
+const (
+	mapKeyProxyPort uint32 = 0
+	mapKeyWgPort    uint32 = 1
+)
+
+//go:generate go run github.com/cilium/ebpf/cmd/bpf2go -cc clang-14 bpf src/portreplace.c --
+
+// EBPF is a wrapper for eBPF program
+type EBPF struct {
+	link link.Link
+}
+
+// NewEBPF create new EBPF instance
+func NewEBPF() *EBPF {
+	return &EBPF{}
+}
+
+// Load load ebpf program
+func (l *EBPF) Load(proxyPort, wgPort int) error {
+	// it required for Docker
+	err := rlimit.RemoveMemlock()
+	if err != nil {
+		return err
+	}
+
+	ifce, err := net.InterfaceByName("lo")
+	if err != nil {
+		return err
+	}
+
+	// Load pre-compiled programs into the kernel.
+	objs := bpfObjects{}
+	err = loadBpfObjects(&objs, nil)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		_ = objs.Close()
+	}()
+
+	err = objs.XdpPortMap.Put(mapKeyProxyPort, uint16(proxyPort))
+	if err != nil {
+		return err
+	}
+
+	err = objs.XdpPortMap.Put(mapKeyWgPort, uint16(wgPort))
+	if err != nil {
+		return err
+	}
+
+	defer func() {
+		_ = objs.XdpPortMap.Close()
+	}()
+
+	l.link, err = link.AttachXDP(link.XDPOptions{
+		Program:   objs.XdpProgFunc,
+		Interface: ifce.Index,
+	})
+	if err != nil {
+		return err
+	}
+
+	return err
+}
+
+// Free free ebpf program
+func (l *EBPF) Free() error {
+	if l.link != nil {
+		return l.link.Close()
+	}
+	return nil
+}