This adds support for setting synthetic NIC MAC address from within Linux
guests. Before using this feature, the option "spoofing of MAC address"
should be enabled at the Hyper-V manager / Settings of the synthetic
NIC.

Thanks to Kin Cho <kcho@infoblox.com> for the initial implementation and
tests. And, thanks to Long Li <longli@microsoft.com> for the debugging
works.
Reported-and-tested-by: Kin Cho <kcho@infoblox.com>
Reported-by: Long Li <longli@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>