msg/async/rdma: Move resource handling to Device

msg/async/rdma: Move resource handling to Device

Move rx/tx completion channel and completion queue from RDMAStack into
Device class
Move SRQ and QP handling from Infiniband into Device class.
Adapt polling() to poll on multiple devices - will be used in a later
commit.

On construction Device will create a completion channel. This will
be done for every HCA on the server.
Only the Device in use will be initialized (init() will be called) and
cq, srq, MemoryManager and the rest of the resources will be allocated.

This patch also introduces RDMADispatcher::poll_{start,stop}
It is being used to stop the polling thread before destructing the
Device resources.

Issue: 995322
Change-Id: I79bfdc687ab690a46c05e271a436b33d8dba0182
Signed-off-by: Amir Vadai <amir@vadai.me>