- Add $netif_ipexpand_max to specify the upper limit for the number of
  addresses generated by an address range specification.  The default
  value is 2048.  This can be increased by setting $netif_ipexpand_max
  in rc.conf.

- Fix warning messages when an address range spec exceeds the upper limit.

PR:	186841
Introduce new scope related functions.

* new macro to remove magic number - IPV6_ADDR_SCOPES_COUNT;
* sa6_checkzone() - this function checks sockaddr_in6 structure
  for correctness of sin6_scope_id. It also can fill correct
  value sometimes.
* in6_getscopezone() - this function returns scope zone id for
  specified interface and scope.
* in6_getlinkifnet() - this function returns struct ifnet for
  corresponding zone id of link-local scope.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC