Fix vmxnet module on kernels >= 3.16

* Add compat check for ethtool_ops in net_device struct.
* SET_ETHTOOL_OPS is no longer defined, but can be manually.
Fix vmhgfs module on kernels >= 3.16

* Use read_iter/write_iter file operations on kernels >= 3.16.
* Do not set aio_read/aio_write on kernels >= 3.16.