net: clean up skb headers code

commit 1a37e412a0225fcba5587 (net: Use 16bits for *_headers
fields of struct skbuff) converts skb->*_header to u16,
some #if NET_SKBUFF_DATA_USES_OFFSET are now useless,
and to be safe, we could just use "X = (typeof(X)) ~0U;"
as suggested by David.

Cc: David S. Miller <davem@davemloft.net>
Cc: Simon Horman <horms@verge.net.au>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f45de07..6b1b52c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -199,9 +199,7 @@
 	skb->truesize = sizeof(struct sk_buff);
 	atomic_set(&skb->users, 1);
 
-#ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
-#endif
+	skb->mac_header = (typeof(skb->mac_header))~0U;
 out:
 	return skb;
 }
@@ -275,10 +273,8 @@
 	skb->data = data;
 	skb_reset_tail_pointer(skb);
 	skb->end = skb->tail + size;
-#ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
-	skb->transport_header = (__u16) ~0U;
-#endif
+	skb->mac_header = (typeof(skb->mac_header))~0U;
+	skb->transport_header = (typeof(skb->transport_header))~0U;
 
 	/* make sure we initialize shinfo sequentially */
 	shinfo = skb_shinfo(skb);
@@ -344,10 +340,8 @@
 	skb->data = data;
 	skb_reset_tail_pointer(skb);
 	skb->end = skb->tail + size;
-#ifdef NET_SKBUFF_DATA_USES_OFFSET
-	skb->mac_header = (__u16) ~0U;
-	skb->transport_header = (__u16) ~0U;
-#endif
+	skb->mac_header = (typeof(skb->mac_header))~0U;
+	skb->transport_header = (typeof(skb->transport_header))~0U;
 
 	/* make sure we initialize shinfo sequentially */
 	shinfo = skb_shinfo(skb);