net: Move skb decrypted field, avoid explicity copy

Commit 784abe24c9 ("net: Add decrypted field to skb")
introduced a 'decrypted' field that is explicitly copied on skb
copy and clone.

Move it between headers_start[0] and headers_end[0], so that we
don't need to copy it explicitly as it's copied by the memcpy()
in __copy_skb_header().

While at it, drop the assignment in __skb_clone(), it was
already redundant.

This doesn't change the size of sk_buff or cacheline boundaries.

The 15-bits hole before tc_index becomes a 14-bits hole, and
will be again a 15-bits hole when this change is merged with
commit 8b7008620b ("net: Don't copy pfmemalloc flag in
__copy_skb_header()").

v2: as reported by kbuild test robot (oops, I forgot to build
    with CONFIG_TLS_DEVICE it seems), we can't use
    CHECK_SKB_FIELD() on a bit-field member. Just drop the
    check for the moment being, perhaps we could think of some
    magic to also check bit-field members one day.

Fixes: 784abe24c9 ("net: Add decrypted field to skb")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -805,9 +805,6 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 	 * It is not yet because we do not want to have a 16 bit hole
 	 */
 	new->queue_mapping = old->queue_mapping;
-#ifdef CONFIG_TLS_DEVICE
-	new->decrypted = old->decrypted;
-#endif
 
 	memcpy(&new->headers_start, &old->headers_start,
 	       offsetof(struct sk_buff, headers_end) -
@@ -868,9 +865,6 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
 	C(head_frag);
 	C(data);
 	C(truesize);
-#ifdef CONFIG_TLS_DEVICE
-	C(decrypted);
-#endif
 	refcount_set(&n->users, 1);
 
 	atomic_inc(&(skb_shinfo(skb)->dataref));