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

This reverts commit 9b001a7d.

It breaks the Android kernel abi, but will be brought in through a
different branch to ensure it ends up in the tree properly.

Bug: 161946584
Change-Id: Ibbe04b272b916b4bc5f8ef681520c7cae4fa87a9
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>