portlist: add Poller.IncludeLocalhost option

This PR parameterizes receiving loopback updates from the portlist package.
Callers can now include services bound to localhost if they want.
Note that this option is off by default still.

Fixes #8171

Signed-off-by: Marwan Sulaiman <marwan@tailscale.com>

portlist/portlist.go

@@ -18,6 +18,7 @@ type Port struct {
 	Proto   string // "tcp" or "udp"
 	Port    uint16 // port number
 	Process string // optional process name, if found
+	Pid     int    // process id, if known
 }
 
 // List is a list of Ports.
@@ -69,12 +70,11 @@ func sortAndDedup(ps List) List {
 	out := ps[:0]
 	var last Port
 	for _, p := range ps {
-		protoPort := Port{Proto: p.Proto, Port: p.Port}
-		if last == protoPort {
+		if last.Proto == p.Proto && last.Port == p.Port {
 			continue
 		}
 		out = append(out, p)
-		last = protoPort
+		last = p
 	}
 	return out
 }