Improve bsbport flash and memory usage

- remove float
- add const where possible
- fix some wrong formated lines
- invert bytes on tcp connection also
- tcp connection now uses same send buffer and send_start  
- fix bsbport_rx_periodic() sometimes to drops a message because lenght byte was not received already
avr is little endian and bsb needs big endian.
tried:
int16_t * tmp = &data[1];
*tmp = ((int32_t) fp_val * 64) / 10;
but it saves no byte eather