[AX25]: Make ax2asc thread-proof

Ax2asc was still using a static buffer for all invocations which isn't
exactly SMP-safe.  Change ax2asc to take an additional result buffer as
the argument.  Change all callers to provide such a buffer.

Signed-off-by: Ralf Baechle DL5RB <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ax25.h b/include/net/ax25.h
index 926eed5..364b046 100644
--- a/include/net/ax25.h
+++ b/include/net/ax25.h
@@ -257,7 +257,7 @@
 
 /* ax25_addr.c */
 extern ax25_address null_ax25_address;
-extern char *ax2asc(ax25_address *);
+extern char *ax2asc(char *buf, ax25_address *);
 extern ax25_address *asc2ax(char *);
 extern int  ax25cmp(ax25_address *, ax25_address *);
 extern int  ax25digicmp(ax25_digi *, ax25_digi *);