net/e1000: fix VF Rx interrupt enabling

net/e1000: fix VF Rx interrupt enabling

When using UIO, after enabling the interrupt to get the PF
message, VF RX queue interrupt is not working.
It's expected, as UIO doesn't support multiple interrupt.
So, PMD should not try to enable RX queue interrupt. Then
APP can know the RX queue interrupt is not enabled and only
choose the polling mode.

Fixes: 316f4f1adc2e ("net/igb: support VF mailbox interrupt for link up/down")
CC: stable@dpdk.org
Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>