Fix up synchronization with WebRTC calls

We were both calling one of the WebRTC functions from the wrong thread
and were modifying data structures from multiple threads simultaneously.

Change-Id: I76c1dd080b8b63d3b1155733f31ee6d1e3b30949
diff --git a/aos/network/BUILD b/aos/network/BUILD
index be7e5eb..b430d90 100644
--- a/aos/network/BUILD
+++ b/aos/network/BUILD
@@ -397,6 +397,7 @@
         ":web_proxy_fbs",
         ":web_proxy_utils",
         "//aos/events:shm_event_loop",
+        "//aos/mutex",
         "//aos/seasocks:seasocks_logger",
         "//third_party:webrtc",
         "//third_party/seasocks",