datapath: Add eventmask support to CT action.

Upstream commit:

    commit 120645513f55a4ac5543120d9e79925d30a0156f
    Author: Jarno Rajahalme <jarno@ovn.org>
    Date:   Fri Apr 21 16:48:06 2017 -0700

    openvswitch: Add eventmask support to CT action.

    Add a new optional conntrack action attribute OVS_CT_ATTR_EVENTMASK,
    which can be used in conjunction with the commit flag
    (OVS_CT_ATTR_COMMIT) to set the mask of bits specifying which
    conntrack events (IPCT_*) should be delivered via the Netfilter
    netlink multicast groups.  Default behavior depends on the system
    configuration, but typically a lot of events are delivered.  This can be
    very chatty for the NFNLGRP_CONNTRACK_UPDATE group, even if only some
    types of events are of interest.

    Netfilter core init_conntrack() adds the event cache extension, so we
    only need to set the ctmask value.  However, if the system is
    configured without support for events, the setting will be skipped due
    to extension not being found.

    Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
    Reviewed-by: Greg Rose <gvrose8192@gmail.com>
    Acked-by: Joe Stringer <joe@ovn.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Joe Stringer <joe@ovn.org>

lib/dpif-netdev.c

@@ -5136,6 +5136,10 @@ dp_execute_cb(void *aux_, struct dp_packet_batch *packets_,
             case OVS_CT_ATTR_LABELS:
                 setlabel = nl_attr_get(b);
                 break;
+            case OVS_CT_ATTR_EVENTMASK:
+                /* Silently ignored, as userspace datapath does not generate
+                 * netlink events. */
+                break;
             case OVS_CT_ATTR_NAT:
             case OVS_CT_ATTR_UNSPEC:
             case __OVS_CT_ATTR_MAX: