tests: Port test-sflow and test-netflow to Windows.

After the change, both of them compile. test-netflow related
unit tests pass.

test-sflow related tests do not pass because
of LOOPBACK_INTERFACE constraints for 'agent'.
(It should be revisited later.)

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
ovs-benchmark: Compile for windows.

This just makes ovs-benchmark compile on windows.
This lets us go ahead with just a 'make' instead of
picking and choosing executables that are tested to work on
windows as arguments for make.

This commit does not make ovs-benchmark a supported utility
on windows.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>