Fix the sense of a test.
diff --git a/print-802_11.c b/print-802_11.c
index a6779a5..196d25c 100644
--- a/print-802_11.c
+++ b/print-802_11.c
@@ -22,7 +22,7 @@
 
 #ifndef lint
 static const char rcsid[] _U_ =
-    "@(#) $Header: /tcpdump/master/tcpdump/print-802_11.c,v 1.39 2005-11-13 19:59:19 guy Exp $ (LBL)";
+    "@(#) $Header: /tcpdump/master/tcpdump/print-802_11.c,v 1.40 2005-11-13 20:03:21 guy Exp $ (LBL)";
 #endif
 
 #ifdef HAVE_CONFIG_H
@@ -196,7 +196,7 @@
 				return;
 			memcpy(&pbody->challenge, p + offset, 2);
 			offset += 2;
-			if (pbody->challenge.length == 0) {
+			if (pbody->challenge.length != 0) {
 				if (pbody->challenge.length > 253)
 					return;
 				if (!TTEST2(*(p + offset), pbody->challenge.length))