Merge branch 'ipv4-invalidate-broadcast-neigh-upon-address-addition'

Ido Schimmel says:

====================
ipv4: Invalidate neighbour for broadcast address upon address addition

Patch #1 solves a recently reported issue [1]. See detailed description
in the changelog.

Patch #2 adds a matching test case.

Targeting at net-next since as far as I can tell this use case never
worked.

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

 # ./fib_tests.sh
 ...
 Tests passed: 186
 Tests failed:   0

[1] https://lore.kernel.org/netdev/55a04a8f-56f3-f73c-2aea-2195923f09d1@huawei.com/
====================

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