openvswitch: switch from WARN to pr_warn

As noted by Paolo Abeni, pr_warn doesn't generate any splat and can still
preserve the warning to the user that feature downgrade occurred.  We
likely cannot introduce other kinds of checks / enforcement here because
syzbot can generate different genl versions to the datapath.

Reported-by: syzbot+31cde0bef4bbf8ba2d86@syzkaller.appspotmail.com
Fixes: 44da5ae5fb ("openvswitch: Drop user features if old user space attempted to create datapath")
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Acked-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/openvswitch/datapath.c

@@ -1616,7 +1616,8 @@ static void ovs_dp_reset_user_features(struct sk_buff *skb,
 	if (IS_ERR(dp))
 		return;
 
-	WARN(dp->user_features, "Dropping previously announced user features\n");
+	pr_warn("%s: Dropping previously announced user features\n",
+		ovs_dp_name(dp));
 	dp->user_features = 0;
 }