ipv4: Fix wrong order of ip_rt_get_source() and update iph->daddr.

ipv4: Fix wrong order of ip_rt_get_source() and update iph->daddr.

This patch fix a bug which introduced by commit ac8a4810 (ipv4: Save
nexthop address of LSRR/SSRR option to IPCB.).In that patch, we saved
the nexthop of SRR in ip_option->nexthop and update iph->daddr until
we get to ip_forward_options(), but we need to update it before
ip_rt_get_source(), otherwise we may get a wrong src.

Signed-off-by: Li Wei <lw@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>