net: core: let's use native isxdigit instead of custom

In kernel we have fast and pretty implementation of the isxdigit() function.
Let's use it.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/utils.c

@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/jiffies.h>
 #include <linux/kernel.h>
+#include <linux/ctype.h>
 #include <linux/inet.h>
 #include <linux/mm.h>
 #include <linux/net.h>
@@ -348,9 +349,7 @@ int mac_pton(const char *s, u8 *mac)
 
 	/* Don't dirty result unless string is valid MAC. */
 	for (i = 0; i < ETH_ALEN; i++) {
-		if (!strchr("0123456789abcdefABCDEF", s[i * 3]))
-			return 0;
-		if (!strchr("0123456789abcdefABCDEF", s[i * 3 + 1]))
+		if (!isxdigit(s[i * 3]) || !isxdigit(s[i * 3 + 1]))
 			return 0;
 		if (i != ETH_ALEN - 1 && s[i * 3 + 2] != ':')
 			return 0;