Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/aos/ipc_lib/shm_observers.cc b/aos/ipc_lib/shm_observers.cc
index 04a6214..2f28e46 100644
--- a/aos/ipc_lib/shm_observers.cc
+++ b/aos/ipc_lib/shm_observers.cc
@@ -1,8 +1,6 @@
 #include "aos/ipc_lib/shm_observers.h"
 
-namespace aos {
-namespace linux_code {
-namespace ipc_lib {
+namespace aos::linux_code::ipc_lib {
 
 ShmAccessorObserver before_observer = nullptr, after_observer = nullptr;
 
@@ -12,6 +10,4 @@
   after_observer = after;
 }
 
-}  // namespace ipc_lib
-}  // namespace linux_code
-}  // namespace aos
+}  // namespace aos::linux_code::ipc_lib