After commit 308edfdf ("gre6: Cleanup GREv6 receive path, call
common GRE functions") it's not used anywhere in the module, but
previously was used in ip6gre_rcv().

Fixes: 308edfdf ("gre6: Cleanup GREv6 receive path, call common GRE functions")
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>