ip6gre: add a rtnl link alias for ip6gretap

With this alias, we don't need to load manually the module before adding an
ip6gretap interface with iproute2.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 5f19dfb..d172ec4 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -1724,4 +1724,5 @@
 MODULE_AUTHOR("D. Kozlov (xeb@mail.ru)");
 MODULE_DESCRIPTION("GRE over IPv6 tunneling device");
 MODULE_ALIAS_RTNL_LINK("ip6gre");
+MODULE_ALIAS_RTNL_LINK("ip6gretap");
 MODULE_ALIAS_NETDEV("ip6gre0");