Update iface.py to fix the error of Interface name

Sometimes, 'bytes' after 'Interface' are too long, and there is no space between 'Interface' and  'bytes'.
For example, in my /proc/net/dev there is one line begin with 'eth0:137719774170', and the iface will be identified as 'eth0:137719774170'.
Merge pull request #157 from Earne/master

Update iface.py to fix the error of Interface name