net: dsa: lan9303: Simplify lan9303_xxx_packet_processing() usage

Simplify usage of lan9303_enable_packet_processing,
lan9303_disable_packet_processing()

Signed-off-by: Egil Hjelmeland <privat@egil-hjelmeland.no>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>