net: mvneta: fix mvneta_config_rss on armada 3700

The mvneta Ethernet driver is used on a few different Marvell SoCs.
Some SoCs have per cpu interrupts for Ethernet events, the driver uses
a per CPU napi structure for this case. Some SoCs such as armada 3700
have a single interrupt for Ethernet events, the driver uses a global
napi structure for this case.

Current mvneta_config_rss() always operates the per cpu napi structure.
Fix it by operating a global napi for "single interrupt" case, and per
cpu napi structure for remaining cases.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Fixes: 2636ac3c ("net: mvneta: Add network support for Armada 3700 SoC")
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>