[Nearby] Fix spacing on data usage dialog.

Increases the margin between the radio buttons on the data usage dialog
to match the UI specs.

Spec:
  carbon.googleplex.com/cros-ux/pages/nearby-share/settings-approach

Screenshot:
  https://screenshot.googleplex.com/8patFRrV2S2u2mw.png

Bug: b:162328100
Change-Id: I7f0096500822cbe7fd0d43c35d2e753b31517f2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461712Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Michael Hansen <hansenmichael@google.com>
Cr-Commit-Position: refs/heads/master@{#815340}

chrome/browser/resources/settings/chromeos/nearby_share_page/nearby_share_data_usage_dialog.html

@@ -12,6 +12,10 @@
 <dom-module id="nearby-share-data-usage-dialog">
   <template>
     <style>
+      cr-radio-button {
+        margin-bottom: 24px;
+      }
+
       .data-usage-name {
         font-weight: 600;
       }