rpcsvc: Fix memory corruption caused by rpcsvc_dump returning non-zero

The convention followed is that any actor should return non-zero
value only if it has not attempted to send the reply back. If an
actor returns non-zero, rpcsvc_handle_rpc_call tries to send an
error reply. Since, rpcsvc_submit_generic frees the rpc_req, its wrong
to invoke it more than once on same rpc_req. When the transport is not
connected, rpcsvc_dump used to pass the non-zero value it got from
 transport to rpcsvc resulting in memory corruption. Hence this patch
makes rpcsvc_dump to return 0.

Change-Id: I1b6f28969ee546c44d193d3d33debccb65585b69
BUG: 903113
Signed-off-by: Raghavendra G <raghavendra@gluster.com>
Reviewed-on: http://review.gluster.org/4183
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>
Reviewed-by: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>