net: mac802154: Introduce a synchronous API for MLME commands

This is the slow path, we need to wait for each command to be processed
before continuing so let's introduce an helper which does the
transmission and blocks until it gets notified of its asynchronous
completion. This helper is going to be used when introducing scan
support.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20220519150516.443078-10-miquel.raynal@bootlin.com


Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>