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_lib.cc b/aos/network/sctp_lib.cc
index 99a7f09..829ae67 100644
--- a/aos/network/sctp_lib.cc
+++ b/aos/network/sctp_lib.cc
@@ -26,8 +26,7 @@
 DEFINE_bool(disable_ipv6, false, "disable ipv6");
 DEFINE_int32(rmem, 0, "If nonzero, set rmem to this size.");
 
-namespace aos {
-namespace message_bridge {
+namespace aos::message_bridge {
 
 namespace {
 const char *sac_state_tbl[] = {"COMMUNICATION_UP", "COMMUNICATION_LOST",
@@ -788,5 +787,4 @@
   }
 }
 
-}  // namespace message_bridge
-}  // namespace aos
+}  // namespace aos::message_bridge