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.
Add netns option to --net switch

Allows attaching an existing network namespace to a container on create.
e.g. --net="netns:my-netns".

Closes #7455

Signed-off-by: Hugo Duncan <hugo@hugoduncan.org>