net/netmon, add: add netmon.State type alias of interfaces.State

... in prep for merging the net/interfaces package into net/netmon.

This is a no-op change that updates a bunch of the API signatures ahead of
a future change to actually move things (and remove the type alias)

Updates tailscale/corp#10910
Updates tailscale/corp#18960
Updates #7967
Updates #3299

Change-Id: I477613388f09389214db0d77ccf24a65bff2199c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/debug.go

@@ -23,7 +23,6 @@ import (
 	"tailscale.com/derp/derphttp"
 	"tailscale.com/health"
 	"tailscale.com/ipn"
-	"tailscale.com/net/interfaces"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/tshttpproxy"
 	"tailscale.com/tailcfg"
@@ -73,7 +72,7 @@ func debugMode(args []string) error {
 }
 
 func runMonitor(ctx context.Context, loop bool) error {
-	dump := func(st *interfaces.State) {
+	dump := func(st *netmon.State) {
 		j, _ := json.MarshalIndent(st, "", "    ")
 		os.Stderr.Write(j)
 	}

cmd/tailscaled/depaware.txt

@@ -295,7 +295,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/net/dnscache                                   from tailscale.com/control/controlclient+
         tailscale.com/net/dnsfallback                                from tailscale.com/cmd/tailscaled+
         tailscale.com/net/flowtrack                                  from tailscale.com/net/packet+
-     💣 tailscale.com/net/interfaces                                 from tailscale.com/cmd/tailscaled+
+     💣 tailscale.com/net/interfaces                                 from tailscale.com/doctor/ethtool+
         tailscale.com/net/netaddr                                    from tailscale.com/ipn+
         tailscale.com/net/netcheck                                   from tailscale.com/wgengine/magicsock+
         tailscale.com/net/neterror                                   from tailscale.com/net/dns/resolver+