DNS forwarder and common ebpf loader (#1083)

In case the 53 UDP port is not an option to bind then we hijack the DNS traffic with eBPF, and we forward the traffic to the listener on a custom port. With this implementation, we should be able to listen to DNS queries on any address and still set the local host system to send queries to the custom address on port 53.

Because we tried to attach multiple XDP programs to the same interface, I did a refactor in the WG traffic forward code also.

client/internal/ebpf/ebpf/manager_linux_test.go

@@ -0,0 +1,40 @@
+package ebpf
+
+import (
+	"testing"
+)
+
+func TestManager_setFeatureFlag(t *testing.T) {
+	mgr := GeneralManager{}
+	mgr.setFeatureFlag(featureFlagWGProxy)
+	if mgr.featureFlags != 1 {
+		t.Errorf("invalid faeture state")
+	}
+
+	mgr.setFeatureFlag(featureFlagDnsForwarder)
+	if mgr.featureFlags != 3 {
+		t.Errorf("invalid faeture state")
+	}
+}
+
+func TestManager_unsetFeatureFlag(t *testing.T) {
+	mgr := GeneralManager{}
+	mgr.setFeatureFlag(featureFlagWGProxy)
+	mgr.setFeatureFlag(featureFlagDnsForwarder)
+
+	err := mgr.unsetFeatureFlag(featureFlagWGProxy)
+	if err != nil {
+		t.Errorf("unexpected error: %s", err)
+	}
+	if mgr.featureFlags != 2 {
+		t.Errorf("invalid faeture state, expected: %d, got: %d", 2, mgr.featureFlags)
+	}
+
+	err = mgr.unsetFeatureFlag(featureFlagDnsForwarder)
+	if err != nil {
+		t.Errorf("unexpected error: %s", err)
+	}
+	if mgr.featureFlags != 0 {
+		t.Errorf("invalid faeture state, expected: %d, got: %d", 0, mgr.featureFlags)
+	}
+}