eventdev: check error in default Rx conf callback

eventdev: check error in default Rx conf callback

The default adapter configuration callback is invoked when a Rx
queue is added to the adapter and the adapter detects that a SW
service is needed. The adapter needs to re-configure the device
with an additional port and to do do, it needs to stop the
device and restart it after it is done reconfiguring it. This
patch adds code to check the return code of
rte_event_dev_start() for both when the reconfiguration fails
and when it succeeds and introduces a new error code (-EIO)
for the first case.

Coverity issue: 257000
Fixes: 9c38b704d280 ("eventdev: add eth Rx adapter implementation")
Cc: stable@dpdk.org
Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>