IPV6_CUSTOM_SCOPES macro

IPV6_CUSTOM_SCOPES: together, the following three macro definitions, ip6_addr_has_scope , ip6_addr_assign_zone , and ip6_addr_test_zone , completely define the lwIP scoping policy. The definitions below implement the default policy from RFC 4007 Sec. 6. Should an implementation desire to implement a different policy, it can define IPV6_CUSTOM_SCOPES to 1 and supply its own definitions for the three macros instead.