Fix the reading of /proc/net/dev

When the bytes received counter gets too big it changes format from
name:  10 ...
name: 100 ...
name:1000 ...

The last one means sscanf can't parse a string and a long seperately - you
just get a string.  Fixed by detecting a char after ':', splitting the name
and reparsing the long.

bug:2612082
Change-Id: I84e41da1e38d24ea61f996ede9c87769abba5d22