ipv4: Remove RTO_ONLINK.

ipv4: Remove RTO_ONLINK.

RTO_ONLINK was a flag used in ->flowi4_tos that allowed to alter the
scope of an IPv4 route lookup. Setting this flag was equivalent to
specifying RT_SCOPE_LINK in ->flowi4_scope.

With commit ec20b2830093 ("ipv4: Set scope explicitly in
ip_route_output()."), the last users of RTO_ONLINK have been removed.
Therefore, we can now drop the code that checked this bit and stop
modifying ->flowi4_scope in ip_route_output_key_hash().

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/57de760565cab55df7b129f523530ac6475865b2.1712754146.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>