Revert "net/ipv6: fix bool/int mismatch for skip_notify_on_dev_down"

This reverts commit 76e38e6e.

It breaks the Android KABI and will be brought back at a later time when
it is safe to do so.

Bug: 161946584
Change-Id: I7d9e90dde9c6fada5013550a7673bf378f3fadcb
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>