net/ixgbe: check for illegal Tx packets

net/ixgbe: check for illegal Tx packets

For ixgbe, there is restriction that data buffers of any transmitted
packet must include at least 12 bytes of the src/dst Ethernet MAC
addresses as well as 2 bytes of the Type/Len field, otherwise, tx hang
would happen.

This patch adds check for those illegal packets and protects TX from
hanging.

Fixes: 7829b8d52be0 ("net/ixgbe: add Tx preparation")
Cc: stable@dpdk.org
Signed-off-by: Xiao Zhang <xiao.zhang@intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Xiaolong Ye <xiaolong.ye@intel.com>