HowTo use AC/DC with sigrok

[Ho-Ro]

From EEVBLOG 6022 thread:

1. change the configuration for 6022BE
   from "ARRAY_AND_SIZE(dc_coupling), FALSE"
   to "ARRAY_AND_SIZE(acdc_coupling), TRUE" in these lines:
   https://github.com/sigrokproject/libsigrok/blob/fb28e72dfdea0d985e03795f1f058aa4621e7e55/src/hardware/hantek-6xxx/api.c#L79
   https://github.com/sigrokproject/libsigrok/blob/fb28e72dfdea0d985e03795f1f058aa4621e7e55/src/hardware/hantek-6xxx/api.c#L86
   (do the same also for BL if needed).

2. change this line
   https://github.com/sigrokproject/sigrok-firmware-fx2lafw/blob/61f1c8fc33ce959f167f6bcb5ba3b0959d60b038/hw/hantek-6022be/fw.c#L29
   from "#define SET_COUPLING(x)" to "#define SET_COUPLING(x) set_coupling(x)"