kernel/core_hook.c: try umount /system/etc/hosts

Modding hosts file is a common thing to have on rooted android devices.
But this is easy to detect, either by reading the file, checking modified time and checking its filesize.
Unmounting it as needed for non-root processes solves this issue.

kernel: try umount /system/etc/hosts
tiann#1494

kernel/core_hook.c

@@ -610,6 +610,9 @@ int ksu_handle_setuid(struct cred *new, const struct cred *old)
 	try_umount("/debug_ramdisk", false, MNT_DETACH);
 	try_umount("/sbin", false, MNT_DETACH);
 
+	// try umount /system/etc/hosts (hosts module)
+	try_umount("/system/etc/hosts", false, MNT_DETACH);
+
 	return 0;
 }