testpmd will initialize default max packet length to 1518 which doesn't
include vlan tag size in ether overheader. Once, send the max mtu length
packet with vlan tag, the max packet length will exceed 1518 that will
cause packets dropped directly from NIC hw side.

e1000 can support single vlan tags that need more 4 bytes for max packet
size, so, configures the correct max packet size in dev_config ops.

Fixes: 35b2d13fd6fd ("net: add rte prefix to ether defines")

Signed-off-by: SteveX Yang <redacted>
---
 drivers/net/e1000/em_ethdev.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/e1000/em_ethdev.c b/drivers/net/e1000/em_ethdev.c
index 1dc360713..485a30625 100644
--- a/drivers/net/e1000/em_ethdev.c
+++ b/drivers/net/e1000/em_ethdev.c

@@ -441,6 +441,12 @@ eth_em_configure(struct rte_eth_dev *dev)
 	PMD_INIT_FUNC_TRACE();
 	intr->flags |= E1000_FLAG_NEED_LINK_UPDATE;
 
+	/**
+	 * Considering vlan tag packet, max frame size should be MTU and
+	 * corresponding ether overhead.
+	 */
+	eth_em_mtu_set(dev, dev->data->mtu);
+
 	PMD_INIT_FUNC_TRACE();
 
 	return 0;

-- 
2.17.1