net/null: fix library version in meson build

Fixes: efd5d1a8d8dd ("drivers/net: build some vdev PMDs with meson")
Cc: stable@dpdk.org

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

drivers/net/null/meson.build

@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: BSD-3-Clause
 # Copyright(c) 2017 Intel Corporation
 
+version = 2
 sources = files('rte_eth_null.c')