Merge branch 'nexthop-blackhole'

Ido Schimmel says:

====================
nexthop: Do not flush blackhole nexthops when loopback goes down

Patch #1 prevents blackhole nexthops from being flushed when the
loopback device goes down given that as far as user space is concerned,
these nexthops do not have a nexthop device.

Patch #2 adds a test case.

There are no regressions in fib_nexthops.sh with this change:

 # ./fib_nexthops.sh
 ...
 Tests passed: 165
 Tests failed:   0
====================

Signed-off-by: David S. Miller <davem@davemloft.net>