dhcpcd: remove advertisement of addresses

dhcpcd: remove advertisement of addresses

Address advertisemnt was used to allow IP address sharing to work.
It also required the DHCP server to allow the same IP for many
hosts, which modern DHCP servers deny you from doing.
Lastly, there are niggles with the implementation that are
impossible to fully fix due to how the various protocols work,
especially ARP.

All platforms dhcpcd supports allow better ways of doing this,
such as bonding (Linux), trunk(4) (OpenBSD), lagg(4) (Other BSDs).

ARP advertisements will only be made when addresses are added
OR defended against for kernels without RFC 5227 support.