lib, net: make isodigit() public and use it

There are at least two users of isodigit(). Let's make it a public
function of ctype.h.

Signed-off-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/ctype.h

···
 	return c | 0x20;
 }
 
+/* Fast check for octal digit */
+static inline int isodigit(const char c)
+{
+	return c >= '0' && c <= '7';
+}
+
 #endif

lib/dynamic_debug.c

···
  * allow the user to express a query which matches a format
  * containing embedded spaces.
  */
-#define isodigit(c)		((c) >= '0' && (c) <= '7')
 static char *unescape(char *str)
 {
 	char *in = str;

net/sunrpc/cache.c

···
  * key and content are both parsed by cache
  */
 
-#define isodigit(c) (isdigit(c) && c <= '7')
 int qword_get(char **bpp, char *dest, int bufsize)
 {
 	/* return bytes copied, or -1 on error */