[IPV6]: Make IPV6_{RECV,2292}RTHDR boolean options.

Because reversing RH0 is no longer supported by deprecation
of RH0, let's make IPV6_{RECV,2292}RTHDR boolean options.
Boolean are more appropriate from standard POV.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>