dhcpsvc: fix interface to match legacy version

internal/dhcpsvc/dhcpsvc.go

@@ -64,8 +64,9 @@ type Interface interface {
 	AddLease(l *Lease) (err error)
 
 	// UpdateStaticLease changes an existing DHCP lease.  It returns an error if
-	// there is no lease equal to old or if new is invalid or already exists.
-	UpdateStaticLease(old, new *Lease) (err error)
+	// there is no lease with such hardware addressor if new values are invalid
+	// or already exist.
+	UpdateStaticLease(l *Lease) (err error)
 
 	// RemoveLease removes an existing DHCP lease.  It returns an error if there
 	// is no lease equal to l.
@@ -112,7 +113,7 @@ func (Empty) Leases() (leases []*Lease) { return nil }
 func (Empty) AddLease(_ *Lease) (err error) { return nil }
 
 // UpdateStaticLease implements the [Interface] interface for Empty.
-func (Empty) UpdateStaticLease(_, _ *Lease) (err error) { return nil }
+func (Empty) UpdateStaticLease(_ *Lease) (err error) { return nil }
 
 // RemoveLease implements the [Interface] interface for Empty.
 func (Empty) RemoveLease(_ *Lease) (err error) { return nil }