ipv6: Add "offload" and "trap" indications to routes

In a similar fashion to previous patch, add "offload" and "trap"
indication to IPv6 routes.

This is done by using two unused bits in 'struct fib6_info' to hold
these indications. Capable drivers are expected to set these when
processing the various in-kernel route notifications.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>