net: hisilicon: Make CONFIG_HNS invisible

The HNS config symbol enables the framework support for the Hisilicon
Network Subsystem.  It is already selected by all of its users, so there
is no reason to make it visible.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>