Neutron Ports: Add support for extra_dhcp_opts

[fatmcgav]

As requested in https://github.com/terraform-providers/terraform-provider-openstack/issues/99, the Ports package should support the extra_dhcp_opts param.

Further details on API available here: https://developer.openstack.org/api-ref/networking/v2/index.html?expanded=create-port-detail

[jtopjian]

Additional work required: Locate where extra_dhcp_opts is defined in Neutron.

Bonus: add extra_dhcp_opts to an existing Port acceptance test and verify it works.

[ozerovandrei]

Hey.
Can I take this one? #533 seems abandoned.
@bugosiphionah can I create a new PR for that issue?

[jtopjian]

@ozerovandrei If you don't hear back from @bugosiphionah in the next day, then I would say you can proceed with working on this.

[ozerovandrei]

Ok. I created some PRs. I've decided to implement it in a separate extension for the networking v2 package, because it's described as an extension both in a documentation and a code:

https://developer.openstack.org/api-ref/network/v2/
https://github.com/openstack/neutron/blob/stable/pike/neutron/extensions/extra_dhcp_opt.py

[jtopjian]

Implemented in #804

@ozerovandrei Thank you for your work with this 😄