In the next patch, we're going to use rt_fill_info() to dump exception
routes upon RTM_GETROUTE with NLM_F_ROOT, meaning userspace is requesting
a dump and not a specific route selection, which in turn implies the input
interface is not relevant. Update rt_fill_info() to handle a NULL
flowinfo.

v7: If fl4 is NULL, explicitly set r->rtm_tos to 0: it's not initialised
    otherwise (spotted by David Ahern)

v6: New patch
Suggested-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NStefano Brivio <sbrivio@redhat.com>
Reviewed-by: NDavid Ahern <dsahern@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>