altos: Variable log rate in full logging code too

With the fixed ADC rate used to get better data during flight, the
logging code now needs to vary the data storage rate so that descent
data is recorded at 10 samples/second while ascent data is recorded at
1 sample per second. Having the logging code do this itself eliminates
any interaction with the flight code.

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