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/network/sctp_server.cc b/aos/network/sctp_server.cc
index f4dba39..7f7a0ae 100644
--- a/aos/network/sctp_server.cc
+++ b/aos/network/sctp_server.cc
@@ -18,8 +18,7 @@
 #include "aos/network/sctp_lib.h"
 #include "aos/unique_malloc_ptr.h"
 
-namespace aos {
-namespace message_bridge {
+namespace aos::message_bridge {
 
 SctpServer::SctpServer(int streams, std::string_view local_host, int local_port,
                        SctpAuthMethod requested_authentication)
@@ -109,5 +108,4 @@
 #endif
 }
 
-}  // namespace message_bridge
-}  // namespace aos
+}  // namespace aos::message_bridge