fix(ldap): do not create interfaces from interface_filter entries (#746)

updateInterfaceLdapFilters saved the matched users with SaveInterface,
which creates the interface when it is missing.

On first start that panics. The sync runs immediately (main.go:85) and
the importer later (main.go:116), so the sync creates a stub row for
every interface_filter key, and the importer, which snapshotted the
interface list before its device round-trips, then fails with "interface
already exists". The window is GetInterfaces plus GetPeers, so a
directory on localhost loses the race and a slower one hides it.

The stub rows are wrong anyway. They have no backend, so a typo in an
interface_filter key quietly created an interface attached to no
controller.

Look the interface up and skip with a warning when it is absent. The
filter is applied on the next sync once the importer has created it. A
lookup error that is not ErrNotFound also skips.

Signed-off-by: clark-ja <37738506+clark-ja@users.noreply.github.com>

internal/app/users/user_manager.go

@@ -40,6 +40,8 @@ type PeerDatabaseRepo interface {
 }
 
 type InterfaceDatabaseRepo interface {
+	// GetInterface returns the interface with the given identifier.
+	GetInterface(ctx context.Context, id domain.InterfaceIdentifier) (*domain.Interface, error)
 	// SaveInterface saves the interface with the given identifier.
 	SaveInterface(ctx context.Context, id domain.InterfaceIdentifier, updateFunc func(i *domain.Interface) (*domain.Interface, error)) error
 }