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
What is stored in p1-4? Sometimes the code checks if all values are zero. Might be a good idea to make this a union to access all four values at once.

union {
  uint8_t raw;
  struct { uint8_t p1, p2, p3, p4; } data;
} p;