tools: fix virtio interface name when binding

tools: fix virtio interface name when binding

The dpdk-devbind.py script does not find/display the ifname for virtio
interfaces since the "net" directory is not directly under the device
directory but rather under a subdirectory.
eg.
> dpdk-devbind.py --status
0000:00:03.0 'Virtio network device' if= drv=virtio-pci unused=

This change searches for the first "net" directory under the device
directory hierarchy.
eg.
0000:00:03.0 'Virtio network device' if=ens3 drv=virtio-pci unused=

Fixes: 629395b063e8 ("igb_uio: remove PCI id table")

Signed-off-by: Gary Mussar <gmussar@ciena.com>
Acked-by: John McNamara <john.mcnamara@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>