Add Mellanox ConnectX-3 NIC support for kernel 6.12 (home-assistant#3969)

PR home-assistant#3775 was mistakenly left out of the jump to the 6.12 kernel

Author: greyltc

buildroot-external/kernel/v6.12.y/device-support-pci.config

@@ -26,6 +26,11 @@ CONFIG_NET_VENDOR_STMICRO=y
 CONFIG_STMMAC_ETH=m
 CONFIG_STMMAC_PCI=m
 
+# Mellanox ConnectX-3 NIC support
+CONFIG_MLX4_EN=m
+# CONFIG_MLX4_DEBUG is not set
+CONFIG_MLX4_CORE_GEN2=y
+
 CONFIG_MEDIA_PCI_SUPPORT=y
 
 # PCI sound drivers