doc: ieee802154: fix driver API

Fixes a few minor documentation issues that slipped through in the
recent large documentation update:
- Fixes the ordering of sections to follow the ordering of the
  correspondig sections in the IEEE 802.15.4 standard.
- Fixes a few note/detail sections that were not recognized as such.
- Removes internal TODO markers from the publicly visible docs.
- Fixes wording and typos in a few instances.

Signed-off-by: Florian Grandel <[email protected]>