nvme-fc: fix module unloads while lports still pending

Current code allows the module to be unloaded even if there are
pending data structures, such as localports and controllers on
the localports, that have yet to hit their reference counting
to remove them.

Fix by having exit entrypoint explicitly delete every controller,
which in turn will remove references on the remoteports and localports
causing them to be deleted as well. The exit entrypoint, after
initiating the deletes, will wait for the last localport to be deleted
before continuing.

Signed-off-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>