Improve refcnt traceability and fix rpc_dplx_unref.

Increase caller location information in SVC_REF, SVC_RELEASE,
and SVC_DESTROY macros.

In addition to location, conditional tracing of caller remote
address and port are added.

Fix lost lock in rpc_dplx_unref.

Signed-off-by: Matt Benjamin <matt@linuxbox.com>