luci-compat: Replace legend element with h3.

The legend HTML element is allowed only as first element in fieldset, so
use h3 instead, which is rendered the same within themes.

Fixed #3149.

Signed-off-by: Oldřich Jedlička <oldium.pro@gmail.com>

modules/luci-compat/luasrc/view/cbi/nsection.htm

@@ -1,7 +1,7 @@
 <% if self:cfgvalue(self.section) then section = self.section %>
 	<div class="cbi-section">
 		<% if self.title and #self.title > 0 then -%>
-			<legend><%=self.title%></legend>
+			<h3><%=self.title%></h3>
 		<%- end %>
 		<% if self.description and #self.description > 0 then -%>
 			<div class="cbi-section-descr"><%=self.description%></div>
@@ -19,7 +19,7 @@
 	<% if self.template_addremove then include(self.template_addremove) else -%>
 	<div class="cbi-section" id="cbi-<%=self.config%>-<%=self.section%>">
 		<% if self.title and #self.title > 0 then -%>
-			<legend><%=self.title%></legend>
+			<h3><%=self.title%></h3>
 		<%- end %>
 		<div class="cbi-section-descr"><%=self.description%></div>
 		<input type="submit" class="btn cbi-button cbi-button-add" name="cbi.cns.<%=self.config%>.<%=self.section%>" value="<%:Add%>" />

modules/luci-compat/luasrc/view/cbi/nullsection.htm

@@ -1,6 +1,6 @@
 <div class="cbi-section">
 	<% if self.title and #self.title > 0 then -%>
-		<legend><%=self.title%></legend>
+		<h3><%=self.title%></h3>
 	<%- end %>
 	<% if self.description and #self.description > 0 then -%>
 		<div class="cbi-section-descr"><%=self.description%></div>

modules/luci-compat/luasrc/view/cbi/tsection.htm

@@ -1,6 +1,6 @@
 <div class="cbi-section" id="cbi-<%=self.config%>-<%=self.sectiontype%>">
 	<% if self.title and #self.title > 0 then -%>
-		<legend><%=self.title%></legend>
+		<h3><%=self.title%></h3>
 	<%- end %>
 	<% if self.error_msg and #self.error_msg > 0 then -%>
 		<div class="cbi-section-error">