vmx: allocate space for network interfaces if needed

vmx: allocate space for network interfaces if needed

Dynamically grow the array of network interfaces for each interface
read, instead of using a single array of size 4.  This way, in the
future it will be easier to not limit the number of network interfaces
(which this patch still does not change).

Signed-off-by: Pino Toscano <ptoscano@redhat.com>