mac80211: make ieee80211_get_hdrlen_from_skb return unsigned

Many callers already expect it to.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 1196de8..f9b391f 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1535,7 +1535,7 @@
  *
  * @skb: the frame
  */
-int ieee80211_get_hdrlen_from_skb(const struct sk_buff *skb);
+unsigned int ieee80211_get_hdrlen_from_skb(const struct sk_buff *skb);
 
 /**
  * ieee80211_get_hdrlen - get header length from frame control