freebsd11_network: Move callout struct definition to _callout.h.

This is how FreeBSD does it.

src/libs/compat/freebsd11_network/compat/sys/_callout.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2018, Haiku, Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef _FBSD_COMPAT_SYS__CALLOUT_H_
+#define _FBSD_COMPAT_SYS__CALLOUT_H_
+
+
+#include <util/list.h>
+#include <sys/queue.h>
+#include <sys/_mutex.h>
+
+
+struct callout {
+	struct list_link	link;
+	bigtime_t			due;
+	uint32				flags;
+
+	void *				c_arg;
+	void				(*c_func)(void *);
+	struct mtx *		c_mtx;
+	int					c_flags;
+};
+
+
+#endif /* _FBSD_COMPAT_SYS__CALLOUT_H_ */

src/libs/compat/freebsd11_network/compat/sys/callout.h

@@ -9,22 +9,7 @@
 
 
 #include <sys/haiku-module.h>
-
+#include <sys/_callout.h>
-#include <sys/queue.h>
-
-#include <util/list.h>
-
-
-struct callout {
-	struct list_link	link;
-	bigtime_t			due;
-	uint32				flags;
-
-	void *				c_arg;
-	void				(*c_func)(void *);
-	struct mtx *		c_mtx;
-	int					c_flags;
-};
 
 
 #define	CALLOUT_MPSAFE			0x0008 /* deprecated */