*: reflect SPEC's DNS changes in implementation

* DNS is now a type which will result in a JSON dictionary in
  configurations and results
* Minor refactoring, making use of type embedding

types/types.go

@@ -61,13 +61,14 @@ type NetConf struct {
 	IPAM struct {
 		Type string `json:"type,omitempty"`
 	} `json:"ipam,omitempty"`
+	DNS DNS `json:"dns"`
 }
 
 // Result is what gets returned from the plugin (via stdout) to the caller
 type Result struct {
 	IP4 *IPConfig `json:"ip4,omitempty"`
 	IP6 *IPConfig `json:"ip6,omitempty"`
-	DNS []string  `json:"dns,omitempty"`
+	DNS DNS       `json:"dns,omitempty"`
 }
 
 func (r *Result) Print() error {
@@ -81,6 +82,14 @@ type IPConfig struct {
 	Routes  []Route
 }
 
+// DNS contains values interesting for DNS resolvers
+type DNS struct {
+	Nameservers []string `json:"nameservers,omitempty"`
+	Domain      string   `json:"domain,omitempty"`
+	Search      []string `json:"search,omitempty"`
+	Options     []string `json:"options,omitempty"`
+}
+
 type Route struct {
 	Dst net.IPNet
 	GW  net.IP