IPv6: fix Routing Header Type 0 handling thinko

Oops, thinko.  The test for accempting a RH0 was exatly the wrong way
around.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>