e1000: do not release queue on alloc error

If igb_alloc_rx_queue_mbufs() would fail to allocate an mbuf for RX queue,
it calls igb_rx_queue_release(rxq).
That causes rxq to be silently freed, without updating
dev->data->rx_queues[].
So any further reference to it will trigger the SIGSEGV.
Same thing in em PMD too.

To fix: igb_alloc_rx_queue_mbufs() should just return an error to the
caller and let upper layer to deal with the probem.
That's what ixgbe PMD is doing right now.

Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>