driver: tun: Use new macro SOCK_IOC_TYPE instead of literal number 0x89

The current codes use _IOC_TYPE(cmd) == 0x89 to check if the cmd is one
socket ioctl command like SIOCGIFHWADDR. But the literal number 0x89 may
confuse readers. So create one macro SOCK_IOC_TYPE to enhance the readability.
Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tun.c

@@ -1985,7 +1985,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	int le;
 	int ret;
 
-	if (cmd == TUNSETIFF || cmd == TUNSETQUEUE || _IOC_TYPE(cmd) == 0x89) {
+	if (cmd == TUNSETIFF || cmd == TUNSETQUEUE || _IOC_TYPE(cmd) == SOCK_IOC_TYPE) {
 		if (copy_from_user(&ifr, argp, ifreq_len))
 			return -EFAULT;
 	} else {

include/uapi/linux/sockios.h

@@ -24,6 +24,8 @@
 #define SIOCINQ		FIONREAD
 #define SIOCOUTQ	TIOCOUTQ        /* output queue size (not sent + not acked) */
 
+#define SOCK_IOC_TYPE	0x89
+
 /* Routing table calls. */
 #define SIOCADDRT	0x890B		/* add routing table entry	*/
 #define SIOCDELRT	0x890C		/* delete routing table entry	*/