openssh: add openwrt failsafe support

Adds failsafe support to the openssh package.
Roughly based on an earlier patch.

Ref: https://github.com/openwrt/openwrt/pull/865


Signed-off-by: Jeff Kletsky <git-commits@allycomm.com>
Signed-off-by: Kyle Copperfield <kmcopper@danwin1210.me>