net: eliminate meaningless memcpy to data in pskb_carve_inside_nonlinear()

The frags of skb_shared_info of the data is assigned in following loop. It
is meaningless to do a memcpy of frags here.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>