bol09: fold the origin requirements in one

This is a commit that will just fold the origin node requirements
under a single list.

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

09-features.md

@@ -64,11 +64,10 @@ The origin node:
     unless indicated that it must set the odd feature bit instead.
   * MUST NOT set feature bits it does not support.
   * MUST NOT set feature bits in fields not specified by the table above.
-  * MUST NOT set both the optional and mandatory field.
+  * MUST NOT set both the optional and mandatory bits.
   * MUST set all transitive feature dependencies.
-
-The origin node MUST support:
-  * `var_onion_optin`
+  * MUST support:
+    * `var_onion_optin`
 
 The receiving node:
   * if both the optional and the mandatory feature its in a pair are set,