FROMGIT: net: avoid one loop iteration in __skb_splice_bits

If *len is equal to 0 at the beginning of __splice_segment
it returns true directly. But when decreasing *len from
a positive number to 0 in __splice_segment, it returns false.
The __skb_splice_bits needs to call __splice_segment again.

Recheck *len if it changes, return true in time.
Reduce unnecessary calls to __splice_segment.

Signed-off-by: Pengtao He <hept.hept.hept@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250819021551.8361-1-hept.hept.hept@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

(cherry picked from commit 8f2c72f2252cf228879de0224d5055470fc20c06
 https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git main)
Change-Id: I7dc42a1ce52c74b947b5bd45fe1aef2a94898b51
Signed-off-by: Pengtao He <hepengtao@xiaomi.com>

net/core/skbuff.c

@@ -3149,7 +3149,9 @@ static bool __splice_segment(struct page *page, unsigned int poff,
 		poff += flen;
 		plen -= flen;
 		*len -= flen;
-	} while (*len && plen);
+		if (!*len)
+			return true;
+	} while (plen);
 
 	return false;
 }