mac80211: add functions to create PS Poll and Nullfunc templates

Some hardware, for example wl1251 and wl1271, handle the transmission
of power save related frames in hardware, but the driver is responsible
for creating the templates. It's better to create the templates in mac80211,
that way all drivers can benefit from this.

Add two new functions, ieee80211_pspoll_get() and ieee80211_nullfunc_get()
which drivers need to call to get the frame. Drivers are also responsible
for updating the templates after each association.

Also new struct ieee80211_hdr_3addr is added to ieee80211.h to make it
easy to calculate length of the Nullfunc frame.

Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 7e5af6d..75f46e2 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1875,6 +1875,36 @@
 }
 
 /**
+ * ieee80211_pspoll_get - retrieve a PS Poll template
+ * @hw: pointer obtained from ieee80211_alloc_hw().
+ * @vif: &struct ieee80211_vif pointer from the add_interface callback.
+ *
+ * Creates a PS Poll a template which can, for example, uploaded to
+ * hardware. The template must be updated after association so that correct
+ * AID, BSSID and MAC address is used.
+ *
+ * Note: Caller (or hardware) is responsible for setting the
+ * &IEEE80211_FCTL_PM bit.
+ */
+struct sk_buff *ieee80211_pspoll_get(struct ieee80211_hw *hw,
+				     struct ieee80211_vif *vif);
+
+/**
+ * ieee80211_nullfunc_get - retrieve a nullfunc template
+ * @hw: pointer obtained from ieee80211_alloc_hw().
+ * @vif: &struct ieee80211_vif pointer from the add_interface callback.
+ *
+ * Creates a Nullfunc template which can, for example, uploaded to
+ * hardware. The template must be updated after association so that correct
+ * BSSID and address is used.
+ *
+ * Note: Caller (or hardware) is responsible for setting the
+ * &IEEE80211_FCTL_PM bit as well as Duration and Sequence Control fields.
+ */
+struct sk_buff *ieee80211_nullfunc_get(struct ieee80211_hw *hw,
+				       struct ieee80211_vif *vif);
+
+/**
  * ieee80211_rts_get - RTS frame generation function
  * @hw: pointer obtained from ieee80211_alloc_hw().
  * @vif: &struct ieee80211_vif pointer from the add_interface callback.