[media] DocBook: better document the DVB-S2 rolloff factor

Instead of using a program listing, use a table and make clearer
what each define means.

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

Documentation/DocBook/media/dvb/dvbproperty.xml

···
 
 	<section id="fe-rolloff-t">
 		<title>fe_rolloff type</title>
-		<programlisting>
-typedef enum fe_rolloff {
-	ROLLOFF_35, /* Implied value in DVB-S, default for DVB-S2 */
-	ROLLOFF_20,
-	ROLLOFF_25,
-	ROLLOFF_AUTO,
-} fe_rolloff_t;
-		</programlisting>
+<table pgwide="1" frame="none" id="fe-rolloff">
+    <title>enum fe_rolloff</title>
+    <tgroup cols="2">
+	&cs-def;
+	<thead>
+	<row>
+	    <entry>ID</entry>
+	    <entry>Description</entry>
+	</row>
+	</thead>
+	<tbody valign="top">
+	<row>
+	    <entry align="char" id="ROLLOFF-35"><constant>ROLLOFF_35</constant></entry>
+	    <entry align="char">Roloff factor: &alpha;=35%</entry>
+	</row><row>
+	    <entry align="char" id="ROLLOFF-20"><constant>ROLLOFF_20</constant></entry>
+	    <entry align="char">Roloff factor: &alpha;=20%</entry>
+	</row><row>
+	    <entry align="char" id="ROLLOFF-25"><constant>ROLLOFF_25</constant></entry>
+	    <entry align="char">Roloff factor: &alpha;=25%</entry>
+	</row><row>
+	    <entry align="char" id="ROLLOFF-AUTO"><constant>ROLLOFF_AUTO</constant></entry>
+	    <entry align="char">Auto-detect the roloff factor.</entry>
+	</row>
+        </tbody>
+    </tgroup>
+</table>
 		</section>
 	</section>
 	<section id="DTV-DISEQC-SLAVE-REPLY">

include/uapi/linux/dvb/frontend.h

···
 
 typedef enum fe_pilot fe_pilot_t;
 
-typedef enum fe_rolloff {
+enum fe_rolloff {
 	ROLLOFF_35, /* Implied value in DVB-S, default for DVB-S2 */
 	ROLLOFF_20,
 	ROLLOFF_25,
 	ROLLOFF_AUTO,
-} fe_rolloff_t;
+};
+
+typedef enum fe_rolloff fe_rolloff_t;
 
 typedef enum fe_delivery_system {
 	SYS_UNDEFINED,