Disable the recalibration guard where new recalibrations are triggered
if we detect a packet too soon after calibrating - we found that this
results in erroneous recalibrations, and if the recalibration failed
then the rest of our badness-detection code will request another.

Add a module option disabling all of the recalibration code, in case
an OLPC deployment thinks all of the workarounds we have are doing
more damage than good and wants to experiment with them all disabled.

Based on work by Paul Fox.
Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>