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/signalfd_test.cc b/aos/ipc_lib/signalfd_test.cc
index 40c0a13..2f349c1 100644
--- a/aos/ipc_lib/signalfd_test.cc
+++ b/aos/ipc_lib/signalfd_test.cc
@@ -5,9 +5,7 @@
 
 #include "aos/testing/test_logging.h"
 
-namespace aos {
-namespace ipc_lib {
-namespace testing {
+namespace aos::ipc_lib::testing {
 
 // Tests in this file use separate threads to isolate all manipulation of signal
 // masks between test cases.
@@ -72,6 +70,4 @@
                "Some other code unblocked one or more of our signals");
 }
 
-}  // namespace testing
-}  // namespace ipc_lib
-}  // namespace aos
+}  // namespace aos::ipc_lib::testing