Disabled STM ethernet driver hardware checksum calculation

No need for driver level hardware IPv4/TCP/UDP/ICMP checksum insertion
since LWIP and nanostack handles those already.

Related to issue: #7227

Author: Mika Leppänen

features/netsocket/emac-drivers/TARGET_STM_EMAC/stm32xx_emac.cpp

@@ -125,7 +125,7 @@ bool STM32_EMAC::low_level_init_successful()
 #endif
     EthHandle.Init.MACAddr = &MACAddr[0];
     EthHandle.Init.RxMode = ETH_RXINTERRUPT_MODE;
-    EthHandle.Init.ChecksumMode = ETH_CHECKSUM_BY_HARDWARE;
+    EthHandle.Init.ChecksumMode = ETH_CHECKSUM_BY_SOFTWARE;
     EthHandle.Init.MediaInterface = ETH_MEDIA_INTERFACE_RMII;
     HAL_ETH_Init(&EthHandle);