net/dns: rename Set to SetDNS in OSConfigurator.

wgengine/router.CallbackRouter needs to support both the Router
and OSConfigurator interfaces, so the setters can't both be called
Set.

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

net/dns/direct.go

@@ -114,7 +114,7 @@ func newDirectManager() directManager {
 	return directManager{}
 }
 
-func (m directManager) Set(config OSConfig) error {
+func (m directManager) SetDNS(config OSConfig) error {
 	// Write the tsConf file.
 	buf := new(bytes.Buffer)
 	writeResolvConf(buf, config.Nameservers, config.Domains)