[malloc] Discard all cached data on shutdown

Allow detection of genuine memory leaks by ensuring that all cached
data is freed on shutdown.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/malloc.c

 	return discarded;
 }
 
+/**
+ * Discard all cached data
+ *
+ */
+static void discard_all_cache ( void ) {
+	unsigned int discarded;
+
+	do {
+		discarded = discard_cache();
+	} while ( discarded );
+}
+
 /**
  * Allocate a memory block
  *
 	.initialise = init_heap,
 };
 
+/**
+ * Discard all cached data on shutdown
+ *
+ */
+static void shutdown_cache ( int booting __unused ) {
+	discard_all_cache();
+}
+
+/** Memory allocator shutdown function */
+struct startup_fn heap_startup_fn __startup_fn ( STARTUP_EARLY ) = {
+	.shutdown = shutdown_cache,
+};
+
 #if 0
 #include <stdio.h>
 /**