*: 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

plugins/main/bridge/bridge.go

@@ -35,11 +35,10 @@ const defaultBrName = "cni0"
 
 type NetConf struct {
 	types.NetConf
-	BrName string   `json:"bridge"`
-	IsGW   bool     `json:"isGateway"`
-	IPMasq bool     `json:"ipMasq"`
-	MTU    int      `json:"mtu"`
-	DNS    []string `json:"dns"`
+	BrName string `json:"bridge"`
+	IsGW   bool   `json:"isGateway"`
+	IPMasq bool   `json:"ipMasq"`
+	MTU    int    `json:"mtu"`
 }
 
 func init() {

plugins/main/ipvlan/ipvlan.go

@@ -31,10 +31,9 @@ import (
 
 type NetConf struct {
 	types.NetConf
-	Master string   `json:"master"`
-	Mode   string   `json:"mode"`
-	MTU    int      `json:"mtu"`
-	DNS    []string `json:"dns"`
+	Master string `json:"master"`
+	Mode   string `json:"mode"`
+	MTU    int    `json:"mtu"`
 }
 
 func init() {

plugins/main/macvlan/macvlan.go

@@ -31,10 +31,9 @@ import (
 
 type NetConf struct {
 	types.NetConf
-	Master string   `json:"master"`
-	Mode   string   `json:"mode"`
-	MTU    int      `json:"mtu"`
-	DNS    []string `json:"dns"`
+	Master string `json:"master"`
+	Mode   string `json:"mode"`
+	MTU    int    `json:"mtu"`
 }
 
 func init() {

plugins/main/ptp/ptp.go

@@ -41,9 +41,8 @@ func init() {
 
 type NetConf struct {
 	types.NetConf
-	IPMasq bool     `json:"ipMasq"`
-	MTU    int      `json:"mtu"`
-	DNS    []string `json:"dns"`
+	IPMasq bool `json:"ipMasq"`
+	MTU    int  `json:"mtu"`
 }
 
 func setupContainerVeth(netns, ifName string, mtu int, pr *types.Result) (string, error) {