that the transmit starts. Or if the maca is in a reception cycle, advance the softclock timeout to now so that transmission starts as soon as possible (immediately if a packet isn't being received or right after reception finishes).
based on commit aac3a355451d899f02737f2907af8c874ee4feba of git://git.devl.org/git/malvira/contiki-mc1322x.git