switching Fpgamode while sniffing with FpgaWriteConfWord() was
sometimes too long so the tag answer start was lost.
Now, (only with FPGA_BITSTREAM_HF_15) with "FPGA_HF_READER_MODE_SNIFF_AMPLITUDE |
FPGA_HF_READER_2SUBCARRIERS_424_484_KHZ": the amplitude is shrank
from its 2 LSB bits and those 2 bits are now used to return the current
frequency. From my tests, this 2 bits reduction does not affect
quality of 1SC sniffing, but it may have slightly reduced the
receiving range.
FPGA FSK decoding code is also improved.