migration/rdma: Pass qemu_file errors across link

If we fail for some reason (e.g. a mismatched RAMBlock)
and it's set the qemu_file error flag, pass that error back to the
peer so it can clean up rather than waiting for some higher level
progress.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Michael R. Hines <michael@hinespot.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>