[vmware] Use driver-private data to hold GuestInfo settings block

[vmware] Use driver-private data to hold GuestInfo settings block

Simplify the per-netdevice GuestInfo settings code by using
driver-private data to hold the settings block, instead of using a
separate allocation.

The settings block (if existent) will be automatically unregistered
when the parent network device settings block is unregistered, and no
longer needs to be separately freed.  The guestinfo_net_remove()
function may therefore be omitted completely.

Signed-off-by: Michael Brown <mcb30@ipxe.org>