ethdev: fix a typo in global API introduction

This patch fixes a typo in the eth device API doc, device
config. not stored between calls to rte_eth_dev_start/stop()
should be restored before a call to rte_eth_dev_start()
instead of after a call to rte_eth_dev_start().

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>