net: cpsw: halt network stack before halting the device during suspend

Move network stack halt APIs before halting the hardware to ensure no
packets are queued to hardware during closing the device during
suspend sequence.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>