Moved user interface processing code from "_nas_user_mngr" into "user_api_receive_and_process" function in user_api.c" file to use it from "nas_ue_task.c".

git-svn-id: http://svn.eurecom.fr/openair4G/trunk@4664 818b1a75-f10b-46b9-bf7c-635c3b92a50f