verbs: don't check the cq if nothing is found

The IB channel uses edge-triggered behavior. We chould poll the
cq until we don't find an event. This fixes it so that we unset
vep->check_cq after not finding an event.

Thanks to Teng Wang <tzw0019@tigermail.auburn.edu> for the simple
test case.
Merge branch 'master' into topic/routing
e2e: add --enable-routing

and have create_endpoint() call the e2e transport
e2e: add routing flag and set it in pingpong.c
e2e: save the e2e routing device

Also, retrieve the real ep before using it

With this commit, create_endpoint() works. Need to work on
connect(), accept(), reject().