net: mac802154: Rename the main tx_work struct

This entry is dedicated to synchronous transmissions done by drivers
without async hook. Make this clearer that this is not a work that any
driver can use by at least prefixing it with "sync_". While at it, let's
enhance the comment explaining why we choose one or the other.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20220519150516.443078-3-miquel.raynal@bootlin.com


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