Terminate serialdump when serial device disconnects
Terminate serialdump when serial device disconnects

The running serialdump does not recover from a disconnected device but
runs indefinitely with outputting anything. This makes it quit with a
proper error message.

MohamedSeliem/contiki,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki