ipv6_opt_accepted() returns a bool, and can use const pointers

ipv6_addr_equal(), ipv6_addr_any(), ipv6_addr_loopback(),
ipv6_addr_orchid() return a bool.
Signed-off-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>