INotify: map address/netmask to cidr while parsing interfaces

INotify: map address/netmask to cidr while parsing interfaces

this allows us to always show the 'address' the 'netmask' and the 'cidr'
both for ipv4 and ipv6

there is a small api change involved in one scenario:
if one manually changed the address to cidr format like
    '10.0.0.4/24'

we now get from the api the parsed values
    addr => 10.0.0.4
    netmask => 24
    cidr => 10.0.0.4/24

instead of
    addr => 10.0.0.4/24
    netmask =>

but i think that circumventing our api when writing the file, but still
relying on the api for reading is not a valid use case, i would argue
that we can change this, especially since we have a new field that
contains that information again (cidr)

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>