To call rte_eth_dev_start() to start a device, this function calls the function
pointer (dev_start) that was registered by the specific device.
rte_eth_dev_start() judges the integer returned from dev_start to continue or
return an error. 

In the driver of VMXNET 3 the vmxnet3_dev_start is the function that needs to
be registered as dev_start, and it called vmxnet3_dev_rxtx_init(). 

In vmxnet3_dev_rxtx_init(), a wrong error code may be thrown after it invokes
vmxnet3_post_rx_bufs() because it negates the error code before returning it*.
It causes rte_eth_dev_start() to give a positive number to the invoker, but it
should be a negative number, as described in the comments.

*: At vmxnet3_rxtx.c:1318