module: add within_module() function

It is just a small optimization that allows to replace few
occurrences of within_module_init() || within_module_core()
with a single call.

Signed-off-by: Petr Mladek <pmladek@suse.cz>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --cc include/linux/module.h
Simple merge

diff --cc kernel/module.c
Simple merge