Show tooltip below for diff view options

So they are not covering the "Next" link.

Bug: Issue 14769
Change-Id: Iafe55f6c6dd70f4b408c78252634f36f8601b09f
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.ts b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.ts
index 9943b58..3ebb58f 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.ts
@@ -34,6 +34,7 @@
     id="sideBySideBtn"
     link=""
     has-tooltip=""
+    position-below="[[showTooltipBelow]]"
     class$="[[_computeSideBySideSelected(mode)]]"
     title="Side-by-side diff"
     aria-pressed="[[isSideBySideSelected(mode)]]"
@@ -45,6 +46,7 @@
     id="unifiedBtn"
     link=""
     has-tooltip=""
+    position-below="[[showTooltipBelow]]"
     title="Unified diff"
     class$="[[_computeUnifiedSelected(mode)]]"
     aria-pressed="[[isUnifiedSelected(mode)]]"