802.15.4 - Beacon frame support

[zephyrbot]

Reported by Gajinder Vij:

Add the means to parse or create Beacon frames.

(Imported from Jira ZEP-885)

[zephyrbot]

by Tomasz Bursztyka:

Beacon frame parsing grounds are already in.

[zephyrbot]

by Tomasz Bursztyka:

basic frame creation in.

[zephyrbot]

by Tomasz Bursztyka:

https://gerrit.zephyrproject.org/r/#/q/status:open+project:zephyr+branch:net+topic:ieee802154_rfd

[zephyrbot]

by Andrei Laperie:

These came with new IP stack merging

[zephyrbot]

by Jing Wang:

Beacon Framework is under IP layer, very low level. It is more reasonable covered by Dev testing.