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: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ip6_gre.c

@@ -1724,4 +1724,5 @@ MODULE_LICENSE("GPL");
 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");