ip6_gre: fix device features for ioctl setup

When ip6gre is created using ioctl, its features, such as
scatter-gather, GSO and tx-checksumming will be turned off:

  # ip -f inet6 tunnel add gre6 mode ip6gre remote fd00::1
  # ethtool -k gre6 (truncated output)
    tx-checksumming: off
    scatter-gather: off
    tcp-segmentation-offload: off
    generic-segmentation-offload: off [requested on]

But when netlink is used, they will be enabled:
  # ip link add gre6 type ip6gre remote fd00::1
  # ethtool -k gre6 (truncated output)
    tx-checksumming: on
    scatter-gather: on
    tcp-segmentation-offload: on
    generic-segmentation-offload: on

This results in a loss of performance when gre6 is created via ioctl.
The issue was found with LTP/gre tests.

Fix it by moving the setup of device features to a separate function
and invoke it with ndo_init callback because both netlink and ioctl
will eventually call it via register_netdevice():

   register_netdevice()
       - ndo_init() callback -> ip6gre_tunnel_init() or ip6gre_tap_init()
           - ip6gre_tunnel_init_common()
                - ip6gre_tnl_init_features()

The moved code also contains two minor style fixes:
  * removed needless tab from GRE6_FEATURES on NETIF_F_HIGHDMA line.
  * fixed the issue reported by checkpatch: "Unnecessary parentheses around
    'nt->encap.type == TUNNEL_ENCAP_NONE'"

Fixes: ac4eb009 ("ip6gre: Add support for basic offloads offloads excluding GSO")
Signed-off-by: NAlexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1014,6 +1014,36 @@ static void ip6gre_tunnel_setup(struct net_device *dev)
 	eth_random_addr(dev->perm_addr);
 }
 
+#define GRE6_FEATURES (NETIF_F_SG |		\
+		       NETIF_F_FRAGLIST |	\
+		       NETIF_F_HIGHDMA |	\
+		       NETIF_F_HW_CSUM)
+
+static void ip6gre_tnl_init_features(struct net_device *dev)
+{
+	struct ip6_tnl *nt = netdev_priv(dev);
+
+	dev->features		|= GRE6_FEATURES;
+	dev->hw_features	|= GRE6_FEATURES;
+
+	if (!(nt->parms.o_flags & TUNNEL_SEQ)) {
+		/* TCP offload with GRE SEQ is not supported, nor
+		 * can we support 2 levels of outer headers requiring
+		 * an update.
+		 */
+		if (!(nt->parms.o_flags & TUNNEL_CSUM) ||
+		    nt->encap.type == TUNNEL_ENCAP_NONE) {
+			dev->features    |= NETIF_F_GSO_SOFTWARE;
+			dev->hw_features |= NETIF_F_GSO_SOFTWARE;
+		}
+
+		/* Can use a lockless transmit, unless we generate
+		 * output sequences
+		 */
+		dev->features |= NETIF_F_LLTX;
+	}
+}
+
 static int ip6gre_tunnel_init_common(struct net_device *dev)
 {
 	struct ip6_tnl *tunnel;
@@ -1048,6 +1078,8 @@ static int ip6gre_tunnel_init_common(struct net_device *dev)
 	if (!(tunnel->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT))
 		dev->mtu -= 8;
 
+	ip6gre_tnl_init_features(dev);
+
 	return 0;
 }
 
@@ -1298,11 +1330,6 @@ static const struct net_device_ops ip6gre_tap_netdev_ops = {
 	.ndo_get_iflink = ip6_tnl_get_iflink,
 };
 
-#define GRE6_FEATURES (NETIF_F_SG |		\
-		       NETIF_F_FRAGLIST |	\
-		       NETIF_F_HIGHDMA |		\
-		       NETIF_F_HW_CSUM)
-
 static void ip6gre_tap_setup(struct net_device *dev)
 {
 
@@ -1383,26 +1410,6 @@ static int ip6gre_newlink(struct net *src_net, struct net_device *dev,
 	nt->net = dev_net(dev);
 	ip6gre_tnl_link_config(nt, !tb[IFLA_MTU]);
 
-	dev->features		|= GRE6_FEATURES;
-	dev->hw_features	|= GRE6_FEATURES;
-
-	if (!(nt->parms.o_flags & TUNNEL_SEQ)) {
-		/* TCP offload with GRE SEQ is not supported, nor
-		 * can we support 2 levels of outer headers requiring
-		 * an update.
-		 */
-		if (!(nt->parms.o_flags & TUNNEL_CSUM) ||
-		    (nt->encap.type == TUNNEL_ENCAP_NONE)) {
-			dev->features    |= NETIF_F_GSO_SOFTWARE;
-			dev->hw_features |= NETIF_F_GSO_SOFTWARE;
-		}
-
-		/* Can use a lockless transmit, unless we generate
-		 * output sequences
-		 */
-		dev->features |= NETIF_F_LLTX;
-	}
-
 	err = register_netdevice(dev);
 	if (err)
 		goto out;