net: remove an assert call in eth_get_gso_type

eth_get_gso_type() routine returns segmentation offload type based on
L3 protocol type. It calls g_assert_not_reached if L3 protocol is
unknown, making the following return statement unreachable. Remove the
g_assert call, it maybe triggered by a guest user.

Reported-by: Gaoning Pan <pgn@zju.edu.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/eth.c

@@ -16,6 +16,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/log.h"
 #include "net/eth.h"
 #include "net/checksum.h"
 #include "net/tap.h"
@@ -71,9 +72,8 @@ eth_get_gso_type(uint16_t l3_proto, uint8_t *l3_hdr, uint8_t l4proto)
             return VIRTIO_NET_HDR_GSO_TCPV6 | ecn_state;
         }
     }
-
-    /* Unsupported offload */
-    g_assert_not_reached();
+    qemu_log_mask(LOG_UNIMP, "%s: probably not GSO frame, "
+        "unknown L3 protocol: 0x%04"PRIx16"\n", __func__, l3_proto);
 
     return VIRTIO_NET_HDR_GSO_NONE | ecn_state;
 }