tls: rx: strp: set the skb->len of detached / CoW'ed skbs

alloc_skb_with_frags() fills in page frag sizes but does not
set skb->len and skb->data_len. Set those correctly otherwise
device offload will most likely generate an empty skb and
hit the BUG() at the end of __skb_nsg().

Fixes: 84c61fe1 ("tls: rx: do not use the standard strparser")
Tested-by: Shai Amiram <samiram@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_strp.c

@@ -56,6 +56,8 @@ static struct sk_buff *tls_strp_msg_make_copy(struct tls_strparser *strp)
 		offset += skb_frag_size(frag);
 	}
 
+	skb->len = strp->stm.full_len;
+	skb->data_len = strp->stm.full_len;
 	skb_copy_header(skb, strp->anchor);
 	rxm = strp_msg(skb);
 	rxm->offset = 0;