freebsd_network: Add stub epoch.h.

We don't have a need for these APIs, so we can leave them as dummies.

src/libs/compat/freebsd_network/compat/sys/epoch.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright 2022, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _FBSD_COMPAT_SYS_EPOCH_H_
+#define _FBSD_COMPAT_SYS_EPOCH_H_
+
+
+struct epoch_tracker {
+	int dummy;
+};
+
+#define NET_EPOCH_ENTER(et)
+#define NET_EPOCH_EXIT(et)
+
+
+#endif	/* _FBSD_COMPAT_SYS_EPOCH_H_ */