iw_cxgb4: Guard against null cm_id in dump_ep/qp

Endpoints that are aborting can have already dereferenced the
cm_id and set ep->com.cm_id to NULL.  So guard against that in
dump_ep() and dump_qp().

Also create a common function for setting up ip address pointers
since the same logic is needed in several places.

Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>