Add util to select preferred IPv6 link-local address

This commit implements link-local IPv6 address selection for APF offload
(e.g., mDNS) based on rfc 3484, Section 5, ensuring correct source
address selection for reply packets.

Test: TH
Change-Id: Ic2bfc2c386ffdc044ade203dd34ebfcdf02c7afa
2 files changed