robustify to drop in radio transmitter after startup

[samfok]

We currently handle starting up receiver module after transmitter and the receiver module starts reading in the middle of a packet. We look for the relatively long time between packets to align to the start of a packet.
However, we do not handle a drop and restart in radio transmission after the receiver module assumes it's aligned. If the receiver hardware cuts off the end of a packet because the transmitter cut out and then restarts because the transmitter restarts, our receiver module will be misaligned. We can check more packet timing to be robust to this.