make queue thread safe in push/pop operation

[iHiroakiKawai]

Two threads are touching on a same queue without a mutex in switch implementation. I observed sometimes queue length becomes negative(INTMAX), which result in infinity loop sometimes, or unexpected behaviors.

[nickkaranatsios]

I prefer option 1) because arc/lib directory should not depend on other directories especially src/switch/data path.Kawai-San could you please fix.