DoH: only use the optional IP to bootstrap resolution

Fixes #100

dnscrypt-proxy/proxy.go

@@ -89,6 +89,9 @@ func (proxy *Proxy) StartProxy() {
 	liveServers, err := proxy.serversInfo.refresh(proxy)
 	if liveServers > 0 {
 		dlog.Noticef("dnscrypt-proxy is ready - live servers: %d", liveServers)
+		if !proxy.xTransport.ignoreSystemDNS {
+			proxy.xTransport.clearCache()
+		}
 		SystemDNotify()
 	} else if err != nil {
 		dlog.Error(err)

dnscrypt-proxy/xtransport.go

@@ -51,6 +51,13 @@ func NewXTransport(timeout time.Duration, useIPv4 bool, useIPv6 bool) *XTranspor
 	return &xTransport
 }
 
+func (xTransport *XTransport) clearCache() {
+	xTransport.cachedIPs.Lock()
+	xTransport.cachedIPs.cache = make(map[string]string)
+	xTransport.cachedIPs.Unlock()
+	dlog.Info("IP cache cleared")
+}
+
 func (xTransport *XTransport) rebuildTransport() {
 	dlog.Debug("Rebuilding transport")
 	if xTransport.transport != nil {