net: fix skb_seq_read returning wrong offset/length for page frag data

When called with a consumed value that is less than skb_headlen(skb)
bytes into a page frag, skb_seq_read() incorrectly returns an
offset/length relative to skb->data. Ensure that data which should come
from a page frag does.
Signed-off-by: Thomas Chenault <thomas_chenault@dell.com>
Tested-by: Shyam Iyer <shyam_iyer@dell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -2288,7 +2288,7 @@ unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
 next_skb:
 	block_limit = skb_headlen(st->cur_skb) + st->stepped_offset;
 
-	if (abs_offset < block_limit) {
+	if (abs_offset < block_limit && !st->frag_data) {
 		*data = st->cur_skb->data + (abs_offset - st->stepped_offset);
 		return block_limit - abs_offset;
 	}