devices: fail optional-802.1X connections if supplicant disappears
802-1x.optional=yes means that NM should tolerate a failure or a timeout of the 802.1X authentication and should keep the connection up. Even if the authentication doesn't succeed, NM keeps the supplicant running so that it can continue trying.
If the supplicant disappears because it crashed or was killed externally, NM should fail the connection so that it can be retried.
The current code is wrong also because after releasing the supplicant interface, it calls wired_auth_cond_fail() which tries to connect a signal to priv->supplicant.iface (which is NULL).