[IPV4]: ip_options_fragment() has no effect on fragmentation

Fix error point to options in ip_options_fragment(). optptr get a
error pointer to the ipv4 header, correct is pointer to ipv4 options.

Signed-off-by: Wei Yongjun <weiyj@soft.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>