tun: Fix code style issues in <linux/if_tun.h>

This fixes the following code style problem:
- WARNING: please, no spaces at the start of a line
- CHECK: Please use a blank line after
function/struct/union/enum declarations

Signed-off-by: Yunjian Wang <[e-mail]>
Reviewed-by: Jiri Pirko <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Acked-by: Jason Wang <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/if_tun.h

···
 #if defined(CONFIG_TUN) || defined(CONFIG_TUN_MODULE)
 struct socket *tun_get_socket(struct file *);
 struct ptr_ring *tun_get_tx_ring(struct file *file);
+
 static inline bool tun_is_xdp_frame(void *ptr)
 {
-       return (unsigned long)ptr & TUN_XDP_FLAG;
+	return (unsigned long)ptr & TUN_XDP_FLAG;
 }
+
 static inline void *tun_xdp_to_ptr(struct xdp_frame *xdp)
 {
-       return (void *)((unsigned long)xdp | TUN_XDP_FLAG);
+	return (void *)((unsigned long)xdp | TUN_XDP_FLAG);
 }
+
 static inline struct xdp_frame *tun_ptr_to_xdp(void *ptr)
 {
-       return (void *)((unsigned long)ptr & ~TUN_XDP_FLAG);
+	return (void *)((unsigned long)ptr & ~TUN_XDP_FLAG);
 }
+
 void tun_ptr_free(void *ptr);
 #else
 #include <linux/err.h>
 #include <linux/errno.h>
 struct file;
 struct socket;
+
 static inline struct socket *tun_get_socket(struct file *f)
 {
 	return ERR_PTR(-EINVAL);
 }
+
 static inline struct ptr_ring *tun_get_tx_ring(struct file *f)
 {
 	return ERR_PTR(-EINVAL);
 }
+
 static inline bool tun_is_xdp_frame(void *ptr)
 {
 	return false;
 }
+
 static inline void *tun_xdp_to_ptr(struct xdp_frame *xdp)
 {
 	return NULL;
 }
+
 static inline struct xdp_frame *tun_ptr_to_xdp(void *ptr)
 {
 	return NULL;
 }
+
 static inline void tun_ptr_free(void *ptr)
 {
 }