Tentative does not mean RTM_DELADDR.

Tentative does not mean RTM_DELADDR.
This fixes RTM address handling on FreeBSD and OpenBSD.

Instead of listening for duplicate address messages for
FreeBSD and OpenBSD simply poll for the address flag changing.
This means less code to maintain and hopefully less error-prone.

Remove dead code which send a DAD as this is, and should,
be done entirely in the kernel.