Mount selinuxfs when other filesystems are mounted

Be consistent when mounting filesystems, and mount selinuxfs
at the same time other filesystems are mounted. In particular,
this ensures that a /sys/fs/selinux/null is available at early
boot, avoiding an unnecessary mknod call.

Change-Id: I01e6b3900f48b4cb3f12d8a928e1e95911524252
diff --git a/init/init.cpp b/init/init.cpp
index 4aef823..9e6143b 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -561,6 +561,7 @@
         #define MAKE_STR(x) __STRING(x)
         mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC));
         mount("sysfs", "/sys", "sysfs", 0, NULL);
+        mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);
     }
 
     // We must have some place other than / to create the device nodes for