net: ethernet: microchip: lan743x: Increase rx ring size to improve rx performance

Increase the rx ring size (LAN743X_RX_RING_SIZE) to improve rx performance on some platforms.
Tested on x86 PC with EVB-LAN7430.
The iperf3.7 TCPIP improved from 881 Mbps to 922 Mbps, and UDP improved from 817 Mbps to 936 Mbps.

Signed-off-by: Yuiko Oshino <yuiko.oshino@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>