Implement low-level Ethernet interface for lwIP

Based on lwip_ethernetif.c skeleton file,
use init, receive and transfer
functionality of SMSC9220 Ethernet driver
for the lightweight IP stack.

Receive mechanism is interrupt driven.

HW buffer sizes:
Tx = 4608 bytes (MTU)
Rx = 10560 bytes

lwIP fine tuning:
mbed-os/features/FEATURE_LWIP/lwip-interface/lwip/src/include/lwip/opt.h

Change-Id: I0ea95650c65fb32cafb5c2d3dde11420c61dba66
Signed-off-by: Gabor Kertesz <[email protected]>

Author: gaborkertesz

features/FEATURE_LWIP/lwip-interface/lwip-eth/arch/TARGET_CM3DS_MPS2/lwipopts_conf.h

@@ -0,0 +1,33 @@
+/* Copyright (c) 2017 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef LWIPOPTS_CONF_H
+#define LWIPOPTS_CONF_H
+
+#define LWIP_TRANSPORT_ETHERNET       1
+
+/* The IEEE 802.3ac standard says the maximum Ethernet frame */
+/* size is 1522 bytes to accommodate the four-byte VLAN tag. */
+#define ETH_MAX_FLEN                  1522u /* recommended size for a VLAN frame */
+
+  /* Maximum Transfer Unit
+   * The IEEE 802.3 specification limits the data portion of the 802.3 frame
+   * to a minimum of 46 and a maximum of 1500 bytes, this is on L3 level.
+   */
+#define ETH_L2_HEADER_LEN             22u
+
+#define ETH_MAX_PAYLOAD_LEN           (ETH_MAX_FLEN - ETH_L2_HEADER_LEN)
+
+#endif /* LWIPOPTS_CONF_H */