utils.network._interfaces_ipconfig(): fix botched singleton tuples

```py
Python 2.7.6 (default, Nov 11 2013, 11:11:46)
>>> # Parentheses don't make tuples. Commas do that.
>>> ('Subnet Mask') == 'Subnet Mask' != ('Subnet Mask',)
True
>>> x = ('Subnet Mask')
>>> type(x)
<type 'str'>
>>> y = ('Subnet Mask',)
>>> type(y)
<type 'tuple'>
>>> # Why this went unnoticed:
>>> key = 'Subnet Mask'
>>> key in ('Subnet Mask')
True
>>> # Why this is problematic:
>>> key = 'Mask'
>>> key in ('Subnet Mask')
True
```