See:

commit 7034ca4dda60f213d2d428da690710da6ea9a8df
Author: Julia Lawall <julia@diku.dk>
Date:   Wed Dec 24 16:24:05 2008 +0100

    Staging: rt2860,rt2870: Correct use of ! and &

On linux kernel for reference, rt3090 needs same fix.

diff -p -up 2009_0612_RT3090_Linux_STA_V2.1.0.0_DPO/os/linux/sta_ioctl.c.orig 2009_0612_RT3090_Linux_STA_V2.1.0.0_DPO/os/linux/sta_ioctl.c
--- 2009_0612_RT3090_Linux_STA_V2.1.0.0_DPO/os/linux/sta_ioctl.c.orig	2009-08-07 18:28:25.000000000 -0300
+++ 2009_0612_RT3090_Linux_STA_V2.1.0.0_DPO/os/linux/sta_ioctl.c	2009-08-07 18:28:11.000000000 -0300
@@ -1840,7 +1840,7 @@ int rt_ioctl_siwencode(struct net_device
             }
         else
 			/* Don't complain if only change the mode */
-		if(!erq->flags & IW_ENCODE_MODE) 
+		if(!(erq->flags & IW_ENCODE_MODE)) 
 		{
 				return -EINVAL;
 		}