ipv6: fix checkpatch errors comments and space

WARNING: please, no space before tabs
WARNING: please, no spaces at the start of a line
ERROR: spaces required around that ':' (ctx:VxW)
ERROR: spaces required around that '>' (ctx:VxV)
ERROR: spaces required around that '>=' (ctx:VxV)

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