[TIPC]: Remove code bloat introduced by print buffer rework

This patch allows the compiler to optimize out any code that tries to
send debugging output to the null print buffer (TIPC_NULL), a capability
that was unintentionally broken during the recent print buffer rework.

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Per Liden <per.liden@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/core.h b/net/tipc/core.h
index 47504ec..d1c3948 100644
--- a/net/tipc/core.h
+++ b/net/tipc/core.h
@@ -83,9 +83,9 @@
 #define warn(fmt, arg...) tipc_printf(TIPC_OUTPUT, KERN_WARNING "TIPC: " fmt, ## arg)
 #define info(fmt, arg...) tipc_printf(TIPC_OUTPUT, KERN_NOTICE "TIPC: " fmt, ## arg)
 
-#define dbg(fmt, arg...)  do {if (DBG_OUTPUT) tipc_printf(DBG_OUTPUT, fmt, ## arg);} while(0)
-#define msg_dbg(msg, txt) do {if (DBG_OUTPUT) tipc_msg_print(DBG_OUTPUT, msg, txt);} while(0)
-#define dump(fmt, arg...) do {if (DBG_OUTPUT) tipc_dump(DBG_OUTPUT, fmt, ##arg);} while(0)
+#define dbg(fmt, arg...)  do {if (DBG_OUTPUT != TIPC_NULL) tipc_printf(DBG_OUTPUT, fmt, ## arg);} while(0)
+#define msg_dbg(msg, txt) do {if (DBG_OUTPUT != TIPC_NULL) tipc_msg_print(DBG_OUTPUT, msg, txt);} while(0)
+#define dump(fmt, arg...) do {if (DBG_OUTPUT != TIPC_NULL) tipc_dump(DBG_OUTPUT, fmt, ##arg);} while(0)
 
 
 /*