usb-mtp: Add support for inotify based file monitoring

usb-mtp: Add support for inotify based file monitoring

For now, we use inotify watches to track only a small number of
events, namely, add, delete and modify. Note that for delete, the kernel
already deactivates the watch for us and we just need to
take care of modifying our internal state.

inotify is a linux only mechanism.

Suggested-by: Gerd Hoffman <kraxel@redhat.com>
Signed-off-by: Bandan Das <bsd@redhat.com>
Message-id: 1448314625-3855-4-git-send-email-bsd@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>