wgengine/magicsock: stop depending on UpdateDst in legacy codepaths.

This makes connectivity between ancient and new tailscale nodes slightly
worse in some cases, but only in cases where the ancient version would
likely have failed to get connectivity anyway.

Signed-off-by: David Anderson <danderson@tailscale.com>

wgengine/magicsock/magicsock_test.go

@@ -1216,7 +1216,7 @@ func testTwoDevicePing(t *testing.T, d *devices) {
 	})
 }
 
-// TestAddrSet tests addrSet appendDests and UpdateDst.
+// TestAddrSet tests addrSet appendDests and updateDst.
 func TestAddrSet(t *testing.T) {
 	tstest.PanicOnLog()
 	rc := tstest.NewResourceCheck()
@@ -1378,7 +1378,7 @@ func TestAddrSet(t *testing.T) {
 				faket = faket.Add(st.advance)
 
 				if st.updateDst != nil {
-					if err := tt.as.UpdateDst(st.updateDst); err != nil {
+					if err := tt.as.updateDst(st.updateDst); err != nil {
 						t.Fatal(err)
 					}
 					continue