staging: lustre: make lustre dependent on LNet

In the case of lustre routers you only need a functioning
LNet stack. Especially since often the routers are very
light weight and want to avoid any addition software that
would create additional pressures on the system.

Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>