net: Set strict_start_type for routes and rules

New userspace on an older kernel can send unknown and unsupported
attributes resulting in an incompelete config which is almost
always wrong for routing (few exceptions are passthrough settings
like the protocol that installed the route).

Set strict_start_type in the policies for IPv4 and IPv6 routes and
rules to detect new, unsupported attributes and fail the route add.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>