resolve: re-create link unicast scopes on reload

resolve: re-create link unicast scopes on reload

On reload, resolved does not apply new DNSSEC= (or DNSOverTLS=) settings
on links, because the link unicast scopes are not re-created. However,
the servers and link states are updated correctly, so resolvectl and link
state files do show the new setting, leading users to believe the change
took effect immediately, the same way `resolvectl dnssec` does.

Fix this by freeing all of the link unicast scopes during reload, so
that they are re-created with the new settings in link_allocate_scopes().

(cherry picked from commit 6d2247208973fd40a4c8f7cc11f11c09470d074c)