mimxrt: Re-Enable eth checksum creation by HW.

The initial problem with a wrong ICMP checksum was caused by
the test code setting a checksum and the HW taking that probably as
the start value and ending up with 0xffff. With a checksum field of 0
set by the test code the HW creates the proper checksum.

ports/mimxrt/eth.c

@@ -285,10 +285,7 @@ void eth_init(eth_t *self, int mac_idx, const phy_operations_t *phy_ops, int phy
     enet_config.miiDuplex = (enet_mii_duplex_t)duplex;
     enet_config.miiMode = kENET_RmiiMode;
     // Enable checksum generation by the ENET controller
-    // Note: Disabled due to problems with the checksum on ICMP requests
-    // Maybe caused by LWIP inserting 0xffff instead of 0x0000
-    // Keep the code for now until it may be fixed.
-    // enet_config.txAccelerConfig = kENET_TxAccelIpCheckEnabled | kENET_TxAccelProtoCheckEnabled;
+    enet_config.txAccelerConfig = kENET_TxAccelIpCheckEnabled | kENET_TxAccelProtoCheckEnabled;
     // Set interrupt
     enet_config.interrupt |= ENET_TX_INTERRUPT | ENET_RX_INTERRUPT;
 
@@ -351,11 +348,6 @@ STATIC err_t eth_netif_init(struct netif *netif) {
         | NETIF_CHECKSUM_CHECK_TCP
         | NETIF_CHECKSUM_CHECK_ICMP
         | NETIF_CHECKSUM_CHECK_ICMP6
-        | NETIF_CHECKSUM_GEN_IP
-        | NETIF_CHECKSUM_GEN_UDP
-        | NETIF_CHECKSUM_GEN_TCP
-        | NETIF_CHECKSUM_GEN_ICMP
-        | NETIF_CHECKSUM_GEN_ICMP6
         );
     return ERR_OK;
 }

ports/mimxrt/lwip_inc/lwipopts.h

@@ -13,11 +13,8 @@
 #define MEM_ALIGNMENT                   4
 
 #define LWIP_CHKSUM_ALGORITHM           3
-// Chksum generaration by HW fails for ICMP
-// Maybe caused by LWIP inserting ffff instead of 0000
 // The checksum flags are set in eth.c
-#define LWIP_CHECKSUM_CTRL_PER_NETIF    0
-#define LWIP_CHECKSUM_ON_COPY           0
+#define LWIP_CHECKSUM_CTRL_PER_NETIF    1
 
 #define LWIP_ARP                        1
 #define LWIP_ETHERNET                   1