[IPV4]: Get rid of redundant IPCB->opts initialisation

Now that we always zero the IPCB->opts in ip_rcv, it is no longer
necessary to do so before calling netif_rx for tunneled packets.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>