dpdk: fix crash with chelsio pmd

dpdk: fix crash with chelsio pmd

cxgbe PMD initializes its control channel as part of dev_configure(),
and trying to get link status prior to it will lead to a crash.

DPDK documentation loosely hints that we should not call any device
function before dev_start(), call link_state() only for the relevant
PMDs.

From DPDK API documentation:
The functions exported by the application Ethernet API to setup a device
designated by its port identifier must be invoked in the following
order:
    rte_eth_dev_configure()
    rte_eth_tx_queue_setup()
    rte_eth_rx_queue_setup()
    rte_eth_dev_start()
Then, the network application can invoke, in any order, the functions
exported by the Ethernet API to get the MAC address of a given device,
to get the speed and the status of a device physical link, to
receive/transmit [burst of] packets, and so on.

Type: fix

Change-Id: I12d2ab4d84e6bd72a9f695447e86f3222929c804
Signed-off-by: Benoît Ganne <bganne@cisco.com>