FS locking and FD counting

First commit fixes a critical bug which can corrupt the file system.

Second commit fixes a bug which leads to failures when accessing more than one file concurrently (as it happens during boot).

epicardium/ble/ble.c

 #include "epicardium.h"
 #include "modules/log.h"
 
-#include "fs_util.h"
+#include "fs/fs_util.h"
 #include "wsf_types.h"
 #include "wsf_buf.h"
 #include "wsf_trace.h"