Fix SBUS serial input

[wimalopaan]

SBUS signals with period <=8ms are not correctly recognized.

The SBUS input processor uses a sample interval of 5ms, therefore it can only detect stream-pauses > 5ms. If SBUS period is < 8ms, the pause is < 5ms and then the SBUS input processor fails to detect this stream pause. This leads to trainer lost.

[wimalopaan]

Channel0: SBUS frame of FS-A8S with about 4ms pause and the cycles the original processSbusInput() gets called. Should be every 5ms, but it is about 2,3ms to 4,7ms:

Demonstrates that the pause detection will not work: the pulses on channel1 shows the call timepoint.

Channel0: SBus frame of FS-A8S with about 4ms pause and new conversion times (channel 1):

Channel0: SBus frame of FS-iA10B with about 4,7ms pause and new conversion times (channel 1):

(original decoding worked with glitches every 30s)

Channel0: SBus frame of R168 with about 6ms pause and new conversion times (channel 1):

(original decoding worked)

[wimalopaan]

Should be fixed in #1462