vmxnet3: prepare for version 7 changes

vmxnet3 is currently at version 6 and this patch initiates the
preparation to accommodate changes for upto version 7. Introduced
utility macros for vmxnet3 version 7 comparison and update Copyright
information.

Signed-off-by: Ronak Doshi <doshir@vmware.com>
Acked-by: Guolin Yang <gyang@vmware.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>