altos: Complete new telemetry switchover

This involved rewriting the GPS code to use the telemetry structures
directly so that a memcpy could be used to transfer the data to the
telemetry packets, saving a bunch of code space, along with fixing up
the gps testing programs to deal with the structure changes.

In addition, the teledongle code needed to have the monitoring code
split into separate radio receiver and USB writer threads as the
packets are now back-to-back, and hence come too fast to wait for the
USB data to be sent to the host after each one.

Signed-off-by: Keith Packard <keithp@keithp.com>