vmxnet3: auto bind support

vmxnet3: auto bind support

For creating the vmxnet3 interface, add the bind option to automatically bind
the pci to vfio-pci module which removes the need for manual bind. Manual bind
still works, should people prefer to go that route.

Change-Id: Ife75926f8755d754a08dd0ecff0f1de326ad5ba1
Signed-off-by: Steven Luong <sluong@cisco.com>