netlink-socket: Use read/write ioctl instead of ReadFile/WriteFile.

The Windows datapath supports a READ/WRITE ioctl instead of ReadFile/WriteFile.
In this change, we update the following:
- WriteFile() in nl_sock_send__() to use DeviceIoControl(OVS_IOCTL_WRITE)
- ReadFile() in nl_sock_recv__() to use DeviceIoControl(OVS_IOCTL_READ)

The WriteFile() call in nl_sock_transact_multiple__() has not been touched
since it is not needed yet.

Main motive for this change is to be able to unblock the DP Dump workflow.

Signed-off-by: Nithin Raju <nithin@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Eitan Eliahu <eliahue@vmware.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>