ftrace: Have the cached module list show in set_ftrace_filter

When writing in a module filter into set_ftrace_filter for a module that is
not yet loaded, it it cached, and will be executed when the module is loaded
(although that is not implemented yet at this commit). Display the list of
cached modules to be traced.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>