ccieth: implement rma_register and deregister
ccieth: remove the user-space rma handle descriptor

It's useless here, and we don't want a round-trip to convert it
into the driver handle. Let the driver use its own descriptor.
ccieth: add rma stub in the driver
ccieth: RMA only on reliable connections
ccieth: CCI_ENTER/EXIT in RMA calls
tests: make the old ccieth debugging a regular test program "loopback"

It builds but does not run during make check because I don't know
if it would work with other drivers.

This loopback test uses a single endpoint, we can't assume whether
the send completion will arrive before or after the recv event,
same for connect done or accept done events.
ccieth: Port the eth CTP to latest rma API
tests/loopback: fix many warnings when the compiler is picky
tests/loopback: add a rma register+deregister