ipv6: fix checkpatch errors of brace and trailing statements

ERROR: open brace '{' following enum go on the same line
ERROR: open brace '{' following struct go on the same line
ERROR: trailing statements should be on next line

Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>