Check the boolean result of nm_platform_link_get_unmanaged, and if it fails,
assume the device is unmanaged.

--- NetworkManager-1.0.4/src/devices/nm-device.c	2015-07-14 12:31:56.000000000 -0400
+++ NetworkManager-1.0.4/src/devices/nm-device.c	2015-07-26 19:49:07.004024031 -0400
@@ -1131,7 +1131,8 @@
 			 * Currently it can happen that NM deletes 127.0.0.1 address. */
 			nm_device_set_initial_unmanaged_flag (self, NM_UNMANAGED_DEFAULT, TRUE);
 		} else if (priv->platform_link_initialized || (priv->is_nm_owned && nm_device_is_software (self))) {
-			nm_platform_link_get_unmanaged (NM_PLATFORM_GET, priv->ifindex, &platform_unmanaged);
+			if (!nm_platform_link_get_unmanaged (NM_PLATFORM_GET, priv->ifindex, &platform_unmanaged))
+				platform_unmanaged = TRUE;
 			nm_device_set_initial_unmanaged_flag (self, NM_UNMANAGED_DEFAULT, platform_unmanaged);
 		} else {
 			/* Hardware and externally-created software links stay unmanaged