batman-adv: Calculate sizeof using variable insead of types

Documentation/CodingStyle recommends to use the form

	p = kmalloc(sizeof(*p), ...);

to calculate the size of a struct and not the version where the struct
name is spelled out to prevent bugs when the type of p changes. This
also seems appropriate for manipulation of buffers when they are
directly associated with p.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
diff --git a/net/batman-adv/unicast.h b/net/batman-adv/unicast.h
index 2ba867c..62f54b9 100644
--- a/net/batman-adv/unicast.h
+++ b/net/batman-adv/unicast.h
@@ -49,7 +49,7 @@
 			uneven_correction = -1;
 	}
 
-	merged_size = (skb->len - sizeof(struct unicast_frag_packet)) * 2;
+	merged_size = (skb->len - sizeof(*unicast_packet)) * 2;
 	merged_size += sizeof(struct unicast_packet) + uneven_correction;
 
 	return merged_size <= mtu;