drivers/net/wan: fix sparse warning: make symbol static

Fix this sparse warning:

drivers/net/wan/x25_asy.c:623:5: warning: symbol 'x25_asy_esc' was not declared. Should it be static?

Signed-off-by: Hannes Eder <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/wan/x25_asy.c

···
   *			STANDARD X.25 ENCAPSULATION		  	 *
   ************************************************************************/
 
-int x25_asy_esc(unsigned char *s, unsigned char *d, int len)
+static int x25_asy_esc(unsigned char *s, unsigned char *d, int len)
 {
 	unsigned char *ptr = d;
 	unsigned char c;