openvswitch: Allow OVS_USERSPACE_ATTR_USERDATA to be variable length.

Until now, the optional OVS_USERSPACE_ATTR_USERDATA attribute had to be
exactly 64 bits long, if it was present.  However, 64 bits is not enough
space to associate as much information with a flow as would be convenient
for some userspace features now under development.  This commit generalizes
the attribute, allowing it to be any length.

This generalization is backward-compatible: if userspace only uses 64-bit
attributes, then it will not see any change in behavior.

CC: Romain Lenglet <rlenglet@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
diff --git a/net/openvswitch/datapath.h b/net/openvswitch/datapath.h
index 031dfbf..9125ad5 100644
--- a/net/openvswitch/datapath.h
+++ b/net/openvswitch/datapath.h
@@ -119,7 +119,7 @@
  * struct dp_upcall - metadata to include with a packet to send to userspace
  * @cmd: One of %OVS_PACKET_CMD_*.
  * @key: Becomes %OVS_PACKET_ATTR_KEY.  Must be nonnull.
- * @userdata: If nonnull, its u64 value is extracted and passed to userspace as
+ * @userdata: If nonnull, its variable-length value is passed to userspace as
  * %OVS_PACKET_ATTR_USERDATA.
  * @pid: Netlink PID to which packet should be sent.  If @pid is 0 then no
  * packet is sent and the packet is accounted in the datapath's @n_lost