This is a list of things that need to be done to get this driver out of the
staging directory.

  - wfx_version.h is still there in order to ensure synchronization with github.
    It can be dropped as soon as development is entirely in kernel

  - I have to take a decision about secure link support. I can:
      - drop completely
      - keep it in an external patch (my preferred option)
      - replace call to mbedtls with kernel crypto API (necessitate a
        bunch of work)
      - pull mbedtls in kernel (non-realistic)

  - mac80211 interface does not (yet) have expected quality to be placed
    outside of staging:
      - Some processings are redundant with mac80211 ones
      - Many members from wfx_dev/wfx_vif can be retrieved from mac80211
        structures
      - Some functions are too complex
      - ...