Mavlink: initialize _ping_stats
Mavlink: initialize _ping_stats

Uninitialized `_ping_stats.last_ping_time` caused ping statistics to be printed even when no ping was received.
PX4/Firmware,krbeverx/Firmware,PX4/Firmware,dagar/Firmware,krbeverx/Firmware,dagar/Firmware,acfloria/Firmware,dagar/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,dagar/Firmware,Aerotenna/Firmware,acfloria/Firmware,Aerotenna/Firmware,dagar/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,krbeverx/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,Aerotenna/Firmware,acfloria/Firmware,Aerotenna/Firmware,PX4/Firmware,acfloria/Firmware