Land #6591, don't require username for wrt110 cmd exec module

modules/exploits/linux/http/linksys_wrt110_cmd_exec.rb

@@ -43,7 +43,7 @@ class Metasploit3 < Msf::Exploit::Remote
       ))
 
     register_options([
-      OptString.new('USERNAME', [ true, 'Valid router administrator username', 'admin']),
+      OptString.new('USERNAME', [ false, 'Valid router administrator username', 'admin']),
       OptString.new('PASSWORD', [ false, 'Password to login with', 'admin']),
       OptAddress.new('RHOST', [true, 'The address of the router', '192.168.1.1']),
       OptInt.new('TIMEOUT', [false, 'The timeout to use in every request', 20])