coinchooser: change "enable_output_value_rounding" default to True

see diff for rationale

electrum/coinchooser.py

@@ -484,7 +484,12 @@ def get_name(config):
 
 def get_coin_chooser(config):
     klass = COIN_CHOOSERS[get_name(config)]
+    # note: we enable enable_output_value_rounding by default as
+    #       - for sacrificing a few satoshis
+    #       + it gives better privacy for the user re change output
+    #       + it also helps the network as a whole as fees will become noisier
+    #         (trying to counter the heuristic that "whole integer sat/byte feerates" are common)
     coinchooser = klass(
-        enable_output_value_rounding=config.get('coin_chooser_output_rounding', False),
+        enable_output_value_rounding=config.get('coin_chooser_output_rounding', True),
     )
     return coinchooser

electrum/gui/qt/settings_dialog.py

@@ -316,7 +316,7 @@ you close all your wallet windows. Use this to keep your local watchtower runnin
 
         def on_outrounding(x):
             self.config.set_key('coin_chooser_output_rounding', bool(x))
-        enable_outrounding = bool(self.config.get('coin_chooser_output_rounding', False))
+        enable_outrounding = bool(self.config.get('coin_chooser_output_rounding', True))
         outrounding_cb = QCheckBox(_('Enable output value rounding'))
         outrounding_cb.setToolTip(
             _('Set the value of the change output so that it has similar precision to the other outputs.') + '\n' +