sdlog2: poll for sensor and replay on Snappy
sdlog2: poll for sensor and replay on Snappy

This brings better performance, so less missed updates on Snappy, as
well as a bit of a cleanup of the poll and orb_copy logic.

darknight-007/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,darknight-007/Firmware,dagar/Firmware,jlecoeur/Firmware,mje-nz/PX4-Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,jlecoeur/Firmware,acfloria/Firmware,krbeverx/Firmware,jlecoeur/Firmware,PX4/Firmware,jlecoeur/Firmware,dagar/Firmware,acfloria/Firmware,dagar/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,dagar/Firmware,Aerotenna/Firmware,acfloria/Firmware,krbeverx/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,mcgill-robotics/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,dagar/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,PX4/Firmware,acfloria/Firmware,darknight-007/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,krbeverx/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,PX4/Firmware,dagar/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,darknight-007/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,mcgill-robotics/Firmware,PX4/Firmware