Reduce overhead of ipfw's me6 opcode.

Skip checks for IPv6 multicast addresses.
Use in6_localip() for global unicast.
And for IPv6 link-local addresses do search in the IPv6 addresses list.
Since LLA are stored in the kernel internal form, use
IN6_ARE_MASKED_ADDR_EQUAL() macro with lla_mask for addresses comparison.
lla_mask has zero bits in the second word, where we keep sin6_scope_id.

Obtained from: Yandex LLC
Sponsored by: Yandex LLC