seccomp: Report number of loaded filters in /proc/$pid/status

A common question asked when debugging seccomp filters is "how many
filters are attached to your process?" Provide a way to easily answer
this question through /proc/$pid/status with a "Seccomp_filters" line.

Signed-off-by: Kees Cook <keescook@chromium.org>

init/init_task.c

@@ -204,6 +204,9 @@ struct task_struct init_task
 #ifdef CONFIG_SECURITY
 	.security	= NULL,
 #endif
+#ifdef CONFIG_SECCOMP
+	.seccomp	= { .filter_count = ATOMIC_INIT(0) },
+#endif
 };
 EXPORT_SYMBOL(init_task);