dccp: Set TOS and routing scope independently for fib lookups.

There's no reason for setting the RTO_ONLINK flag in ->flowi4_tos as
RT_CONN_FLAGS() does. We can easily set ->flowi4_scope properly
instead. This makes the code more explicit and will allow to convert
->flowi4_tos to dscp_t in the future.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>