Naive GigE implementation

[WhiteBlackGoose]

Notes

• It is only a partial implementation of GigE. Actually, a tiny bit of it, because only the following features are supported:
  • Single link mode
  • Single interface mode
  • One streaming channel
  • Image as payload
  • No H264 or multi-zone support
  • No request of the lost packets

It is however enough for the camera I need, and maybe I'll extend it if I get another camera which needs something beyond that.

• The purpose of this PR is to share my work, in case someone's use case is exactly the same as mine (simple GigE cameras)

• This PR is based on Y-Nak's work (and in fact, by far most of the work belongs to this person, I just finished the streaming part for my use case)

• I didn't name my commits properly because if I'm actually to finish this PR so we could merge it, I'd imagine I'd need to squash and rewrite them many times because I expect quite a fair bit of feedback/change requests from the maintainer

• GigE Example App

• Check test_all.sh is passed. Answer: It doesn't, but it's not my fault

• Add fix #{ISSUE_NUMBER} if the corresponding issue exists.

• Fill out ## Changelog section. If the change is for only internal use, please write None to the section.

Changelog

• gige::enumerate_cameras requires an IP address of the host to listen to cameras from
• Very naive GigE implemented