Merge branch 'ipv4-fix-route-update-on-metric-change'

Paolo Abeni says:

====================
ipv4: fix route update on metric change.

This fixes connected route update on some edge cases for ip addr metric
change.
It additionally includes self tests for the covered scenarios. The new tests
fail on unpatched kernels and pass on the patched one.

v1 -> v2:
 - add selftests
====================

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