When looking up route for destination with rules with
source address restrictions, we may need to find a source
address for the traffic if not given.
Based on patch from Noriaki TAKAMIYA <takamiya@po.ntts.co.jp>.
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>