mac80211: make it work with 3.18.12+

3.18.12 backported 61ada528dea028331e99e8ceaed87c683ad25de2 ("sched/wait:
Provide infrastructure to deal with nested blocking") from 3.19, causing
the following error on load:

[   13.588000] compat: exports duplicate symbol woken_wake_function (owned by kernel)

Fix this by guarding it with a check for 3.18.11 or earlier instead of
3.19.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>

SVN-Revision: 45710

package/kernel/mac80211/patches/311-mac80211-remove-drop_unencrypted-code.patch

@@ -108,7 +108,8 @@ Signed-off-by: Johannes Berg <johannes.berg@intel.com>
  		 (key = rcu_dereference(tx->sdata->default_unicast_key)))
  		tx->key = key;
 -	else if (info->flags & IEEE80211_TX_CTL_INJECTED)
--		tx->key = NULL;
++	else
+ 		tx->key = NULL;
 -	else if (!tx->sdata->drop_unencrypted)
 -		tx->key = NULL;
 -	else if (tx->skb->protocol == tx->sdata->control_port_protocol)
@@ -119,8 +120,7 @@ Signed-off-by: Johannes Berg <johannes.berg@intel.com>
 -		tx->key = NULL;
 -	else if (ieee80211_is_mgmt(hdr->frame_control) &&
 -		 !ieee80211_is_robust_mgmt_frame(tx->skb))
-+	else
- 		tx->key = NULL;
+-		tx->key = NULL;
 -	else {
 -		I802_DEBUG_INC(tx->local->tx_handlers_drop_unencrypted);
 -		return TX_DROP;