conf-parser: distinguish between multiple sections with the same name

conf-parser: distinguish between multiple sections with the same name

Pass on the line on which a section was decleared to the parsers, so they
can distinguish between multiple sections (if they chose to). Currently
no parsers take advantage of this, but a follow-up patch will do that
to distinguish

[Address]
Address=192.168.0.1/24
Label=one

[Address]
Address=192.168.0.2/24
Label=two

from

[Address]
Address=192.168.0.1/24
Label=one
Address=192.168.0.2/24
Label=two