Add AOS message to update sctp auth key in message_bridge

Message bridge now listens to /aos aos.message_bridge.SctpConfig
channel to update the SCTP authentication key. This change only takes
effect if `--wants_sctp_authentication=true` and the kernel supports
SCTP authentication.

Change-Id: Id9e743471668cd26892a12e4fc9b03a73445df10
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/network/message_bridge_server.cc b/aos/network/message_bridge_server.cc
index 449333a..be6cc8e 100644
--- a/aos/network/message_bridge_server.cc
+++ b/aos/network/message_bridge_server.cc
@@ -10,6 +10,9 @@
 
 DEFINE_string(config, "aos_config.json", "Path to the config.");
 DEFINE_int32(rt_priority, -1, "If > 0, run as this RT priority");
+DEFINE_bool(
+    wants_sctp_authentication, false,
+    "When set, try to use SCTP authentication if provided by the kernel");
 
 namespace aos {
 namespace message_bridge {
@@ -25,7 +28,10 @@
     event_loop.SetRuntimeRealtimePriority(FLAGS_rt_priority);
   }
 
-  MessageBridgeServer app(&event_loop, Sha256(config.span()));
+  MessageBridgeServer app(&event_loop, Sha256(config.span()),
+                          FLAGS_wants_sctp_authentication
+                              ? SctpAuthMethod::kAuth
+                              : SctpAuthMethod::kNoAuth);
 
   logging::DynamicLogging dynamic_logging(&event_loop);