Fix adb leaking file descriptors to forked processes

accept() creates a new file descriptor that should be closed on exec so
that forked processes don't keep a fd opened on the socket.

This also fixes b/3297070 where adb hangs after running adb on the
target.

Change-Id: I8df511289e5549ae49b4824c9dfb71a3bf85eae8
diff --git a/adb/jdwp_service.c b/adb/jdwp_service.c
index 296f718..cd62b55 100644
--- a/adb/jdwp_service.c
+++ b/adb/jdwp_service.c
@@ -499,6 +499,7 @@
 
     /* only wait for incoming connections */
     fdevent_add(control->fde, FDE_READ);
+    close_on_exec(s);
 
     D("jdwp control socket started (%d)\n", control->listen_socket);
     return 0;