ethdev: account for smaller MTU when setting default

[ upstream commit da266c6556d22b470679484b62e3f9db192e4032 ]

Currently, if not specified in the user configuration,
rte_eth_dev_configure() sets the MTU of the device to RTE_EHTER_MTU.

This value could potentially be larger than the MTU that the device
supports. This change updates the configured MTU to be the minimum of
the maximum supported MTU and the default DPDK MTU.

Fixes: 1bb4a52 ("ethdev: fix max Rx packet length")

Signed-off-by: Joshua Washington <joshwash@google.com>
Signed-off-by: Rushil Gupta <rushilg@google.com>
Acked-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Acked-by: Ajit Khaparde <ajit.khaparde@broadcom.com>

lib/ethdev/rte_ethdev.c

@@ -1528,7 +1528,9 @@ rte_eth_dev_configure(uint16_t port_id, uint16_t nb_rx_q, uint16_t nb_tx_q,
 	}
 
 	if (dev_conf->rxmode.mtu == 0)
-		dev->data->dev_conf.rxmode.mtu = RTE_ETHER_MTU;
+		dev->data->dev_conf.rxmode.mtu =
+			(dev_info.max_mtu == 0) ? RTE_ETHER_MTU :
+			RTE_MIN(dev_info.max_mtu, RTE_ETHER_MTU);
 
 	ret = eth_dev_validate_mtu(port_id, &dev_info,
 			dev->data->dev_conf.rxmode.mtu);