Shrink /dev/shm/aos_shared_mem

We aren't using it for anything more than AOS_LOG, and the rates on that
are significantly down.  Free up some memory.

Change-Id: I37adeb93b36323011c7d2f0b28b49c9e63ba85c4
diff --git a/aos/ipc_lib/shared_mem.cc b/aos/ipc_lib/shared_mem.cc
index 3bb7267..461e254 100644
--- a/aos/ipc_lib/shared_mem.cc
+++ b/aos/ipc_lib/shared_mem.cc
@@ -18,7 +18,7 @@
 #define AOS_SHM_NAME "/aos_shared_mem"
 // Size of the shared mem segment.
 // This must fit in the tmpfs for /dev/shm/
-#define SIZEOFSHMSEG (4096 * 0x3000)
+#define SIZEOFSHMSEG (4096 * 0x800)
 
 void init_shared_mem_core(aos_shm_core *shm_core) {
   memset(&shm_core->time_offset, 0 , sizeof(shm_core->time_offset));