Even on RTN_ROOT node, we need to process its subtree first.
Fix NULL pointer dereference in fib6_locate().

Based on MIPL2 kernel patch.
Signed-off-by: NYOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: NVille Nuorvala <vnuorval@tcs.hut.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>