altosui: Respect storage limits in flight log max config

altosui: Respect storage limits in flight log max config

Compute the maximum flight log using the data returned from the 'f'
command (total storage and erase block size). Limit menu to choices
which fall within this limit, complain if the user asks for too big a value.

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