ntb_netdev: Fix module_init problem

With both the ntb_transport_init and the ntb_netdev_init_module routines in the
module_init init group, the ntb_netdev_init_module routine can be called before
the ntb_transport_init routine that it depends on is called.  To assure the
proper initialization order put ntb_netdev_init_module in the late_initcall
group.

Fixes runtime errors where the ntb_netdev_init_module call fails with ENODEV.

Signed-off-by: Geoff Levand <geoff@infradead.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>