openvswitch: add erspan version I and II support

The patch adds support for openvswitch to configure erspan
v1 and v2.  The OVS_TUNNEL_KEY_ATTR_ERSPAN_OPTS attr is added
to uapi as a binary blob to support all ERSPAN v1 and v2's
fields.  Note that Previous commit "openvswitch: Add erspan tunnel
support." was reverted since it does not design properly.

Signed-off-by: William Tu <u9012063@gmail.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>