I have an application where ear contains both ejbs and a .war file.
Now suppose if I have 10 entity beans and 10 session beans in my application then according to my understanding I think my ejb module should contain 20 submodule of beans.
First go and read chapter 4 of Better Builds With Maven. That chapter covers this topic rather nicely.
Also, you do not need to place each EJB in its own project. You should group EJBs in projects in a way that makes sense from a component point of view. Also, you would not create multiple subprojects under an ejb subproject, but rather have multiple ejb subprojects. Example: