This reverts the following three commits:
70af921db6799977d9aaf1705ec197
The feature was ill conceived, has terrible semantics, and has added
nothing but regressions to the already fragile ipv6 stack.
Fixes: f1705ec197 ("net: ipv6: Make address flushing on ifdown optional")
Signed-off-by: David S. Miller <davem@davemloft.net>