hw/net: e1000: Remove the logic of padding short frames in the receive path

Now that we have implemented unified short frames padding in the
QEMU networking codes, remove the same logic in the NIC codes.

This actually reverts commit 78aeb23ede.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/e1000.c

@@ -888,7 +888,6 @@ e1000_receive_iov(NetClientState *nc, const struct iovec *iov, int iovcnt)
     uint16_t vlan_special = 0;
     uint8_t vlan_status = 0;
     uint8_t min_buf[ETH_ZLEN];
-    struct iovec min_iov;
     uint8_t *filter_buf = iov->iov_base;
     size_t size = iov_size(iov, iovcnt);
     size_t iov_ofs = 0;
@@ -905,15 +904,7 @@ e1000_receive_iov(NetClientState *nc, const struct iovec *iov, int iovcnt)
         return 0;
     }
 
-    /* Pad to minimum Ethernet frame length */
-    if (size < sizeof(min_buf)) {
-        iov_to_buf(iov, iovcnt, 0, min_buf, size);
-        memset(&min_buf[size], 0, sizeof(min_buf) - size);
-        min_iov.iov_base = filter_buf = min_buf;
-        min_iov.iov_len = size = sizeof(min_buf);
-        iovcnt = 1;
-        iov = &min_iov;
-    } else if (iov->iov_len < MAXIMUM_ETHERNET_HDR_LEN) {
+    if (iov->iov_len < MAXIMUM_ETHERNET_HDR_LEN) {
         /* This is very unlikely, but may happen. */
         iov_to_buf(iov, iovcnt, 0, min_buf, MAXIMUM_ETHERNET_HDR_LEN);
         filter_buf = min_buf;