net/netmon: make ChangeFunc's signature take new ChangeDelta, not bool

Updates #9040

Change-Id: Ia43752064a1a6ecefc8802b58d6eaa0b71cf1f84
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/local.go

@@ -50,6 +50,7 @@ import (
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/dnsfallback"
 	"tailscale.com/net/interfaces"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/netns"
 	"tailscale.com/net/netutil"
 	"tailscale.com/net/tsaddr"
@@ -342,7 +343,7 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 	b.prevIfState = netMon.InterfaceState()
 	// Call our linkChange code once with the current state, and
 	// then also whenever it changes:
-	b.linkChange(false, netMon.InterfaceState())
+	b.linkChange(&netmon.ChangeDelta{New: netMon.InterfaceState()})
 	b.unregisterNetMon = netMon.RegisterChangeCallback(b.linkChange)
 
 	b.unregisterHealthWatch = health.RegisterWatcher(b.onHealthChange)
@@ -508,11 +509,11 @@ func (b *LocalBackend) pauseOrResumeControlClientLocked() {
 }
 
 // linkChange is our network monitor callback, called whenever the network changes.
-// major is whether ifst is different than earlier.
-func (b *LocalBackend) linkChange(major bool, ifst *interfaces.State) {
+func (b *LocalBackend) linkChange(delta *netmon.ChangeDelta) {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
+	ifst := delta.New
 	hadPAC := b.prevIfState.HasPAC()
 	b.prevIfState = ifst
 	b.pauseOrResumeControlClientLocked()