all: move network monitoring from wgengine/monitor to net/netmon

We're using it in more and more places, and it's not really specific to
our use of Wireguard (and does more just link/interface monitoring).

Also removes the separate interface we had for it in sockstats -- it's
a small enough package (we already pull in all of its dependencies
via other paths) that it's not worth the extra complexity.

Updates #7621
Updates #7850

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

net/dns/manager.go

@@ -18,12 +18,12 @@ import (
 	"golang.org/x/exp/slices"
 	"tailscale.com/health"
 	"tailscale.com/net/dns/resolver"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/types/dnstype"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/dnsname"
-	"tailscale.com/wgengine/monitor"
 )
 
 var (
@@ -64,14 +64,14 @@ type Manager struct {
 }
 
 // NewManagers created a new manager from the given config.
-func NewManager(logf logger.Logf, oscfg OSConfigurator, linkMon *monitor.Mon, dialer *tsdial.Dialer, linkSel resolver.ForwardLinkSelector) *Manager {
+func NewManager(logf logger.Logf, oscfg OSConfigurator, netMon *netmon.Monitor, dialer *tsdial.Dialer, linkSel resolver.ForwardLinkSelector) *Manager {
 	if dialer == nil {
 		panic("nil Dialer")
 	}
 	logf = logger.WithPrefix(logf, "dns: ")
 	m := &Manager{
 		logf:     logf,
-		resolver: resolver.New(logf, linkMon, linkSel, dialer),
+		resolver: resolver.New(logf, netMon, linkSel, dialer),
 		os:       oscfg,
 	}
 	m.ctx, m.ctxCancel = context.WithCancel(context.Background())