* constify argument of in6_addrscope();
* use IN6_IS_ADDR_XXX() macro instead of hardcoded values;
* for multicast addresses just return scope value, the only exception
  is addresses with 0x0F scope value (RFC 4291 p2.7.0);

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC
Rename pmap_kenter_temp to pmap_kenter_temporary to be consistent with the
other architectures with this function.

Submitted by:	Svatopluk Kraus <onwahe at gmail.com>
Submitted by:	Michal Meloun <meloun at miracle.cz>
- 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
* use M_ZERO flag with malloc instead of explicit zeroing.
* remove MULTI_SCOPE ifdef.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC
Add const qualifier to in6_addrhash() function.
Add in6ifa_ifwithaddr() function. It is similar to ifa_ifwithaddr,
but does fast lookup in the hash of inet6 addresses.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC