Merge branch 'nexthop-flags' into next

Ido Schimmel  says:

====================

From: Ido Schimmel <idosch@nvidia.com>

Patch #1 prints the recently added 'RTNH_F_TRAP' flag.

Patch #2 makes sure that nexthop flags are always printed for nexthop
objects. Even when the nexthop does not have a device, such as a
blackhole nexthop or a group.

Example output with netdevsim:

$ ip nexthop
id 1 via 192.0.2.2 dev eth0 scope link trap
id 2 blackhole trap
id 3 group 2 trap

Example output with mlxsw:

$ ip nexthop
id 1 via 192.0.2.2 dev swp3 scope link offload
id 2 blackhole offload
id 3 group 2 offload

Tested with fib_nexthops.sh that uses "ip nexthop" output:

Tests passed: 164
Tests failed:   0

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Signed-off-by: David Ahern <dsahern@gmail.com>