ipv6: Simplify link-local address generation for IPv6 GRE.

Since commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
generation."), addrconf_gre_config() has stopped handling IP6GRE
devices specially and just calls the regular addrconf_addr_gen()
function to create their link-local IPv6 addresses.

We can thus avoid using addrconf_gre_config() for IP6GRE devices and
use the normal IPv6 initialisation path instead (that is, jump directly
to addrconf_dev_config() in addrconf_init_auto_addrs()).

See commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
generation.") for a deeper explanation on how and why GRE devices
started handling their IPv6 link-local address generation specially,
why it was a problem, and why this is not even necessary in most cases
(especially for GRE over IPv6).

Signed-off-by: Guillaume Nault <[e-mail]>
Reviewed-by: Ido Schimmel <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

net/ipv6/addrconf.c

···
 	}
 }
 
-#if IS_ENABLED(CONFIG_IPV6_SIT) || IS_ENABLED(CONFIG_NET_IPGRE) || IS_ENABLED(CONFIG_IPV6_GRE)
+#if IS_ENABLED(CONFIG_IPV6_SIT) || IS_ENABLED(CONFIG_NET_IPGRE)
 static void add_v4_addrs(struct inet6_dev *idev)
 {
 	struct in6_addr addr;
···
 	    (dev->type != ARPHRD_IEEE1394) &&
 	    (dev->type != ARPHRD_TUNNEL6) &&
 	    (dev->type != ARPHRD_6LOWPAN) &&
+	    (dev->type != ARPHRD_IP6GRE) &&
 	    (dev->type != ARPHRD_TUNNEL) &&
 	    (dev->type != ARPHRD_NONE) &&
 	    (dev->type != ARPHRD_RAWIP)) {
···
 }
 #endif
 
-#if IS_ENABLED(CONFIG_NET_IPGRE) || IS_ENABLED(CONFIG_IPV6_GRE)
+#if IS_ENABLED(CONFIG_NET_IPGRE)
 static void addrconf_gre_config(struct net_device *dev)
 {
 	struct inet6_dev *idev;
···
 	 * which is in EUI64 mode (as __ipv6_isatap_ifid() would fail in this
 	 * case). Such devices fall back to add_v4_addrs() instead.
 	 */
-	if (!(dev->type == ARPHRD_IPGRE && *(__be32 *)dev->dev_addr == 0 &&
+	if (!(*(__be32 *)dev->dev_addr == 0 &&
 	      idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_EUI64)) {
 		addrconf_addr_gen(idev, true);
 		return;
···
 		addrconf_sit_config(dev);
 		break;
 #endif
-#if IS_ENABLED(CONFIG_NET_IPGRE) || IS_ENABLED(CONFIG_IPV6_GRE)
-	case ARPHRD_IP6GRE:
+#if IS_ENABLED(CONFIG_NET_IPGRE)
 	case ARPHRD_IPGRE:
 		addrconf_gre_config(dev);
 		break;