I am not quite sure if you can switched it on in axis2.xml. But something that woked for me is rampart modules.
You will need to include security modules Rampart along with with Axis 2. Look into http://wso2.org/library/3190#Step_3._Engaging_Rampart_and_setting_authentication_information
You will also uncomment some code in tomcat/other app server's server.xml.
To follow the tutorial which also talk about user name token authentication, which you may leave out just use the SSL part.
You will need to edit the META-INF/services.xml in server to add these policy. Here Your concern should be
which defines ssl, you can remove the
which is used for user name token.