Replace RW lock with mutex, shared_mutex

Test: built, flashed, booted
      system/netd/tests/runtests.sh passes
Change-Id: I42b52d815b6ba0ba6f93dc27e83a900d2abec715
diff --git a/server/FirewallController.h b/server/FirewallController.h
index 8a222d3..9b0c013 100644
--- a/server/FirewallController.h
+++ b/server/FirewallController.h
@@ -17,12 +17,11 @@
 #ifndef _FIREWALL_CONTROLLER_H
 #define _FIREWALL_CONTROLLER_H
 
+#include <mutex>
 #include <set>
 #include <string>
 #include <vector>
 
-#include <utils/RWLock.h>
-
 #include "NetdConstants.h"
 
 enum FirewallRule { DENY, ALLOW };
@@ -75,7 +74,7 @@
 
     static const char* ICMPV6_TYPES[];
 
-    android::RWLock lock;
+    std::mutex lock;
 
 protected:
     friend class FirewallControllerTest;