altos: Improve TM v1.0 apogee estimate

v1.0 boards have noisy accelerometer data caused by interactions
between RF transmission and the accelerometer measurements; this noise
generates a negative bias in the accelerometer readings. The net
effect is that the estimated speed is lower than the actual speed,
causing early an apogee estimate.

By increasing the sigma value for accelerometer data, the kalman
filter 'trusts' the acceleration data less, putting more weight on the
barometer data. This causes the estimated time of apogee to be closer
to the correct value.

This reduces the response to changes in acceleration.

This new value is applied solely to TeleMetrum v1.0 boards. v1.1
boards correct for this error, and hence can use the correct sigma
value for the accelerometer.

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