conf: making MYSQL_DB var as an env

Signed-off-by: Mohammed Ismail <mohammed.ismail@openairinterface.org>

etc/udr.conf

@@ -23,6 +23,6 @@ UDR =
     MYSQL_SERVER = "@MYSQL_IPV4_ADDRESS@"; # YOUR MYSQL DB ADDRESS HERE
     MYSQL_USER   = "@MYSQL_USER@";         # YOUR MYSQL USER HERE
     MYSQL_PASS   = "@MYSQL_PASS@";         # YOUR MYSQL PASSWORD HERE
-    MYSQL_DB     = "MYSQL_DB";             # YOUR DATA BASE NAME HERE
+    MYSQL_DB     = "@MYSQL_DB@";             # YOUR DATA BASE NAME HERE
   };
 };