ft4: Fix incorrect DTCS handling

This driver has been broken forever in how it handles DTCS tone mode.
It was always using the rx_dtcs field, which should only be honored
in a ->DTCS cross mode. The new GUI, being in hide-unused-fields mode
always made this clear, as it appeared to be snapping back to 023
always when the user selected a different value.

Note that the test is *also* broken, which I will fix at the end of
this series.

Related to #11506

chirp/drivers/ft4.py

@@ -1030,7 +1030,7 @@ def encode_sql(self, mem, chan):
         if mem.tmode == "TSQL":
             chan.tx_ctcss = chan.rx_ctcss  # CHIRP uses ctone for TSQL
         if mem.tmode == "DTCS":
-            chan.tx_dcs = chan.rx_dcs     # CHIRP uses rx_dtcs for DTCS
+            chan.rx_dcs = chan.tx_dcs     # CHIRP uses rx_dtcs for DTCS
         # select the correct internal dictionary and key
         mode_dict, key = [
             (TONE_DICT, mem.tmode),