Make the SocketListener control pipe O_CLOEXEC.

Children of processes that use SocketListener should not be able
to stop the SocketListener.

Test: builds, boots
Test: atest libsysutils_tests
Test: atest --test-mapping system/netd
Change-Id: I64898d9966f62004468b8e8a43b59be4a81a8cc4

libsysutils/src/SocketListener.cpp

@@ -95,7 +95,7 @@ int SocketListener::startListener(int backlog) {
     } else if (!mListen)
         mClients[mSock] = new SocketClient(mSock, false, mUseCmdNum);
 
-    if (pipe(mCtrlPipe)) {
+    if (pipe2(mCtrlPipe, O_CLOEXEC)) {
         SLOGE("pipe failed (%s)", strerror(errno));
         return -1;
     }