eal/bsd: fix virtio on FreeBSD

eal/bsd: fix virtio on FreeBSD

Closing /dev/io fd causes SIGBUS in inb/outb instructions
as the process loses the IOPL privileges once the fd is closed:
(gdb) bt
0  0x0000000000492f2c in outb (port=49170, data=0 '\000')
at /usr/include/machine/cpufunc.h:244
1  0x0000000000492f7a in outb_p (data=0 '\000', port=49170)
at /dpdk/dpdk-2.0.0/lib/librte_pmd_virtio/virtio_pci.h:211
2  0x000000000049328d in vtpci_set_status (hw=0x80331f380, status=0 '\000')
at /dpdk/dpdk-2.0.0/lib/librte_pmd_virtio/virtio_pci.c:130
3  0x00000000004931fe in vtpci_reset (hw=0x80331f380)
at /dpdk/dpdk-2.0.0/lib/librte_pmd_virtio/virtio_pci.c:108
4  0x00000000004a175e in eth_virtio_dev_init (eth_dev=0x831b80 <rte_eth_devices>)
at /dpdk/dpdk-2.0.0/lib/librte_pmd_virtio/virtio_ethdev.c:1150
5  0x0000000000462c09 in rte_eth_dev_init (pci_drv=0x79d1a0 <rte_virtio_pmd>,
pci_dev=0x802417560) at /dpdk/dpdk-2.0.0/lib/librte_ether/rte_ethdev.c:326
6  0x000000000046f03f in rte_eal_pci_probe_one_driver (dr=0x79d1a0 <rte_virtio_pmd>,
dev=0x802417560) at /dpdk/dpdk-2.0.0/lib/librte_eal/bsdapp/eal/eal_pci.c:487
7  0x0000000000475b06 in pci_probe_all_drivers (dev=0x802417560)
at /dpdk/dpdk-2.0.0/lib/librte_eal/common/eal_common_pci.c:116
8  0x0000000000475bb9 in rte_eal_pci_probe ()
at /dpdk/dpdk-2.0.0/lib/librte_eal/common/eal_common_pci.c:246
9  0x000000000046cd63 in rte_eal_init (argc=5, argv=0x7fffffffeaf0)
at /dpdk/dpdk-2.0.0/lib/librte_eal/bsdapp/eal/eal.c:554
10 0x0000000000404544 in main ()

Fixes: 8a312224bcde ("eal/bsd: fix fd leak")

Signed-off-by: Raz Amir <razamir22@gmail.com>
Reviewed-by: Bruce Richardson <bruce.richardson@intel.com>