In the listener & aggregator, the signal strength is stored as an
unsigned byte. To display the actual (negative) value, one must
substract 256 (0x100) to the unsigned value.
This commit changes several things:
- Use the decimal (256) instead of the hexadecimal value (0x100).
- Don't substract 256 when copying the value to another unsigned byte
(aggregator).
- Be careful with the type length. In the positioning server, a SS
could be copied to a signed byte, while (theoretically) the negative
value can exceed the capacity of the signed byte. measurement.hh now
defines a type ss_t to store a signal strength value with the good
size (it is currently an int_fast16_t).