net: ip: always cancel IPv6 DAD when address is removed

If the address was removed immediately after being added (e.g. because the
interface MAC address is changed on boot), it would remain in the DAD timer
list.

In one scenario, the DAD timeout would eventually fire, causing the
now-removed address to be modified, potentially causing issues that way.

In another scenario, if the interface was immediately brought back up
again with a different link-local address, this new address would reuse the
first address slot on the interface. Starting the DAD process for this new
address would lead to the same address slot being added to the DAD timer
list a second time, causing an infinite list and associated lockup during
iteration.

Always remove the address from the DAD timer list when it is removed from
the interface, not just when DAD fails.

Signed-off-by: Armin Brauns <armin.brauns@embedded-solutions.at>