ofnet: Initialize structs in bootpath parser

ofnet: Initialize structs in bootpath parser

Code later on checks if variables inside the struct are
0 to see if they have been set, like if there were addresses
in the bootpath.

The variables were not initialized however, so the check
might succeed with uninitialized data, and a new interface
with random addresses and the same name is added. This causes
$net_default_mac to point to the random one, so, for example,
using that variable to load per-mac config files fails.

Bug-Ubuntu: https://bugs.launchpad.net/bugs/1785859

Signed-off-by: Julian Andres Klode <julian.klode@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>