vmxnet3: prepare for version 3 changes

vmxnet3 is currently at version 2, but some command definitions from
previous vmxnet3 versions are missing. Add those definitions before
moving to version 3.

Also, introduce utility macros for vmxnet3 version comparison and update
Copyright information and Maintained by.

Signed-off-by: Shrikrishna Khare <skhare@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>