net/cxgbe: avoid polling link status before device start
net/cxgbe: avoid polling link status before device start

Link updates come in firmware event queue, which is only created
when device starts. So, don't poll for link status if firmware
event queue is not yet created.

This fixes NULL dereference when accessing non existent firmware
event queue.

Fixes: 265af08e75ba ("net/cxgbe: add link up and down ops")
Cc: stable@dpdk.org

Signed-off-by: Rahul Lakkireddy <3a6b348815dc68871481a310c146a6b821ba8f72@chelsio.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk