Complete redesign of the BPSK decoder
This commit implements a new approach for the BPSK AX.25 decoding. It seems that the GNU Radio equalizers (both CMA and LMS) are not ideal for bursty transmissions. After they loose 'lock', they tend to converge quite slow again. The equalizing problem is again solved using an AGC2 block. However, the placement of this block is quite critical. In older versions the AGC was placed several steps after resampling and filtering. This resulted to poor equalization and noise increase. Now the AGC is placed as early as possible when the signal has a large span.