route: label externally offloaded routes

route: label externally offloaded routes

On ip route print dump, label externally offloaded routes with "external".
Offloaded routes are flagged with RTNH_F_EXTERNAL, a recent additon to
net-next.  For example:

$ ip route
default via 192.168.0.2 dev eth0
11.0.0.0/30 dev swp1  proto kernel  scope link  src 11.0.0.2 external
11.0.0.4/30 via 11.0.0.1 dev swp1  proto zebra  metric 20 external
11.0.0.8/30 dev swp2  proto kernel  scope link  src 11.0.0.10 external
11.0.0.12/30 via 11.0.0.9 dev swp2  proto zebra  metric 20 external
12.0.0.2  proto zebra  metric 30 external
        nexthop via 11.0.0.1  dev swp1 weight 1
        nexthop via 11.0.0.9  dev swp2 weight 1
12.0.0.3 via 11.0.0.1 dev swp1  proto zebra  metric 20 external
12.0.0.4 via 11.0.0.9 dev swp2  proto zebra  metric 20 external
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.15

Signed-off-by: Scott Feldman <sfeldma@gmail.com>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>