Avoid NPE when quickly toggling USB debugging state

If you try to disable USB debugging before the socket
to listen is opened in the thread, it will end up
with an NPE.

Do some locking around socket creation and closing
to avoid this.

Bug: 18708503
Change-Id: Iac43e4806fff1e411772b1ba1a070d8a7c776fcb
1 file changed