b43legacy: drop packets we are not able to encrypt

We must drop any packets we are not able to encrypt.
We must not send them unencrypted or with an all-zero-key (which
basically is the same as unencrypted, from a security point of view).

This might only trigger shortly after resume before mac80211 reassociated
and reconfigured the keys.

It is safe to drop these packets, as the association they belong to
is not guaranteed anymore anyway.
This is a security fix in the sense that it prevents information leakage.

This patch by Michael Buesch has been ported to b43legacy.

Cc: Michael Buesch <mb@bu3sch.de>
Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/b43legacy/xmit.h b/drivers/net/wireless/b43legacy/xmit.h
index 8a155d0..bab4792 100644
--- a/drivers/net/wireless/b43legacy/xmit.h
+++ b/drivers/net/wireless/b43legacy/xmit.h
@@ -76,7 +76,7 @@
 
 
 
-void b43legacy_generate_txhdr(struct b43legacy_wldev *dev,
+int b43legacy_generate_txhdr(struct b43legacy_wldev *dev,
 			      u8 *txhdr,
 			      const unsigned char *fragment_data,
 			      unsigned int fragment_len,