IPAllocator: Ensure the allocated IPs are within network range.

Since it is possible to request a specific IP, IPAllocator has to verify
that the request is within boundaries.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>
Merge pull request #8200 from aluzzardi/f-ipallocator-check-range

IPAllocator: Ensure the allocated IPs are within network range.