test_recv_lengths
API CHANGE, new version (api 4, lib 0.5)
 - Receive buffers are now in a shared receive queue.
   The client side stays exactly the same.
   The server side needs to post buffers only once per nic
   (suggested use of msk_getpd, which holds a private pointer for application use and is a per nic variable)
 - Irrelevant to the change, but "msk_ctx" are now completely lockless.
   (internally, receive contexts are per nic as well)
trans_rdma: remove HAS_*_LOCKS flags since all code paths are the same now