net/memif: remove unnecessary Rx interrupt stub

net/memif: remove unnecessary Rx interrupt stub

The code in memif driver to stub out rx_irq_enable is unnecessary
and causes different error returns than other drivers.
The core ethdev code will return -ENOTSUP if the driver has
a null rx_queue_intr_enable callback.

Fixes: 09c7e63a71f9 ("net/memif: introduce memory interface PMD")
Cc: stable@dpdk.org
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>