ipv6:remove useless check

After switch (rthdr->type) {...},the check below is completely useless.Because:
if the type is 2,then hdrlen must be 2 and segments_left must be 1,clearly the
check is redundant;if the type is not 2,then goto sticky_done,the check is useless
too.

Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
Reviewed-by: Shan Wei <shanwei@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>