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.cc b/aos/ipc_lib/signalfd.cc
index f23d0be..d25151d 100644
--- a/aos/ipc_lib/signalfd.cc
+++ b/aos/ipc_lib/signalfd.cc
@@ -12,8 +12,7 @@
 
 #include "glog/logging.h"
 
-namespace aos {
-namespace ipc_lib {
+namespace aos::ipc_lib {
 namespace {
 
 // Wrapper which propagates msan information.
@@ -118,5 +117,4 @@
   return result;
 }
 
-}  // namespace ipc_lib
-}  // namespace aos
+}  // namespace aos::ipc_lib