Merge branch 'route-add-support-and-selftests-for-directed-broadcast-forwarding'

Xin Long says:

====================
route: add support and selftests for directed broadcast forwarding

Patch 1/2 is the feature and 2/2 is the selftest. Check the changelog
on each of them to know the details.

v1->v2:
  - fix a typo in changelog.
  - fix an uapi break that Davide noticed.
  - flush route cache when bc_forwarding is changed.
  - add the selftest for this patch as Ido's suggestion.

v2->v3:
  - fix an incorrect 'if check' in devinet_conf_proc as David Ahern
    noticed.
  - extend the selftest after one David Ahern fix for vrf.

v3->v4:
  - improve the output log in the selftest as David Ahern suggested.
====================

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