Non posso provare ptm, con atm ed eth l'mtu lo setta in automatico (pppoe 1492) ed è OK UP . Se viene impostato in wan lo setta con -8 (es 1492-8=1484) OK UP. Il problema credo che derivi dalle device bcmvopi rimosse che sono impostate da qualche parte, che pur con il wansensing continua a cercare.
[ 530.506000] [ERROR vlan] bcmVlan_setDscpToPbitsTable,2861: Real Device atm_8_35 has no VLAN Interfaces
[ 530.517000] [ERROR vlan] vlanIoctl ,904: Failed to set DSCP to PBITS table entry: atm_8_35, dscp 46, pbits 5
[ 530.552000] [ERROR vlan] bcmVlan_setDscpToPbitsTable,2861: Real Device atm_8_81 has no VLAN Interfaces
[ 530.563000] [ERROR vlan] vlanIoctl ,904: Failed to set DSCP to PBITS table entry: atm_8_81, dscp 46, pbits 5
[ 530.597000] [ERROR vlan] bcmVlan_setDscpToPbitsTable,2861: Real Device ptm0 has no VLAN Interfaces
[ 530.607000] [ERROR vlan] vlanIoctl ,904: Failed to set DSCP to PBITS table entry: ptm0, dscp 46, pbits 5
root@OpenWrt:~#