Author: Neil Brown

Define module_put_and_exit() and use it for nfsd/lockd

Both nfsd and lockd have threads which expect to hold a reference
to the module while the thread is running.  In order for the thread
to be able to put_module() the module before exiting, the
put_module code must be call from outside the module.

This patch provides module_put_and_exit in non-modular code which a
thread-in-a-module can call.  It also gets nfsd and lockd to use it
as appropriate.

Note that in lockd, we can __get_module in the thread itself as the
creator of the thread is waiting for the thread to startup.

In nfsd and for the 'reclaimer' threaded started by locked, we
__get_module first and put_module if the thread failed to start.