tailcfg, all: use []netip.AddrPort instead of []string for Endpoints

It's JSON wire compatible.

Updates #cleanup

Change-Id: Ifa5c17768fec35b305b06d75eb5f0611c8a135a6
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tailcfg/tailcfg_test.go

@@ -466,13 +466,13 @@ func TestNodeEqual(t *testing.T) {
 			true,
 		},
 		{
-			&Node{Endpoints: []string{}},
+			&Node{Endpoints: []netip.AddrPort{}},
 			&Node{Endpoints: nil},
 			false,
 		},
 		{
-			&Node{Endpoints: []string{}},
-			&Node{Endpoints: []string{}},
+			&Node{Endpoints: []netip.AddrPort{}},
+			&Node{Endpoints: []netip.AddrPort{}},
 			true,
 		},
 		{
@@ -677,7 +677,7 @@ func TestCloneNode(t *testing.T) {
 		{"zero_fields", &Node{
 			Addresses:  make([]netip.Prefix, 0),
 			AllowedIPs: make([]netip.Prefix, 0),
-			Endpoints:  make([]string, 0),
+			Endpoints:  make([]netip.AddrPort, 0),
 		}},
 	}
 	for _, tt := range tests {