all: use any instead of interface{}

My favorite part of generics.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

wgengine/monitor/monitor.go

@@ -340,7 +340,7 @@ func (m *Mon) debounce() {
 	}
 }
 
-func jsonSummary(x interface{}) interface{} {
+func jsonSummary(x any) any {
 	j, err := json.Marshal(x)
 	if err != nil {
 		return err

wgengine/monitor/monitor_darwin.go

@@ -178,7 +178,7 @@ func ipOfAddr(a route.Addr) netaddr.IP {
 	return netaddr.IP{}
 }
 
-func fmtAddr(a route.Addr) interface{} {
+func fmtAddr(a route.Addr) any {
 	if a == nil {
 		return nil
 	}