tipc: delete the unlikely branch in tipc_aead_encrypt

When a skb comes to tipc_aead_encrypt(), it's always linear. The
unlikely check 'skb_cloned(skb) && tailen <= skb_tailroom(skb)'
can completely be taken care of in skb_cow_data() by the code
in branch "if (!skb_has_frag_list())".

Also, remove the 'TODO:' annotation, as the pages in skbs are not
writable, see more on commit 3cf4375a ("tipc: do not write
skb_shinfo frags when doing decrytion").
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Jon Maloy <jmaloy@redhat.com>
Link: https://lore.kernel.org/r/47a478da0b6095b76e3cbe7a75cbd25d9da1df9a.1637773872.git.lucien.xin@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/tipc/crypto.c

@@ -761,21 +761,10 @@ static int tipc_aead_encrypt(struct tipc_aead *aead, struct sk_buff *skb,
 			 skb_tailroom(skb), tailen);
 	}
 
-	if (unlikely(!skb_cloned(skb) && tailen <= skb_tailroom(skb))) {
-		nsg = 1;
-		trailer = skb;
-	} else {
-		/* TODO: We could avoid skb_cow_data() if skb has no frag_list
-		 * e.g. by skb_fill_page_desc() to add another page to the skb
-		 * with the wanted tailen... However, page skbs look not often,
-		 * so take it easy now!
-		 * Cloned skbs e.g. from link_xmit() seems no choice though :(
-		 */
-		nsg = skb_cow_data(skb, tailen, &trailer);
-		if (unlikely(nsg < 0)) {
-			pr_err("TX: skb_cow_data() returned %d\n", nsg);
-			return nsg;
-		}
+	nsg = skb_cow_data(skb, tailen, &trailer);
+	if (unlikely(nsg < 0)) {
+		pr_err("TX: skb_cow_data() returned %d\n", nsg);
+		return nsg;
 	}
 
 	pskb_put(skb, trailer, tailen);