xapi mod: add comma after space

************* Module salt.modules.xapi
C0324:722,16:vm_netstats._info: Comma not followed by a space
                ret[vif_rec['device']] = _get_metrics_record(xapi,'VIF',
                                                                 ^^
                                                            vif_rec)
Merge pull request #5227 from cvrebert/patch-3

xapi mod: add comma after space