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).

https://bugzilla.redhat.com/show_bug.cgi?id=1934291
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/776
(cherry picked from commit 840e54a96c)
(cherry picked from commit b4ba6e7af5)

src/devices/nm-device-ethernet.c

@@ -726,7 +726,9 @@ supplicant_iface_state_cb(NMSupplicantInterface *iface,
 
     if (new_state == NM_SUPPLICANT_INTERFACE_STATE_DOWN) {
         supplicant_interface_release(self);
-        wired_auth_cond_fail(self, NM_DEVICE_STATE_REASON_SUPPLICANT_FAILED);
+        nm_device_state_changed(NM_DEVICE(self),
+                                NM_DEVICE_STATE_FAILED,
+                                NM_DEVICE_STATE_REASON_SUPPLICANT_FAILED);
         return;
     }