Handle "weave expose" in weaver

The change makes "weave expose" to call the "/expose" HTTP
endpoint implemented in router which exposes the bridge.

Such architectural change required as we need to know whether NPC is
enabled when exposing the bridge and weaver knows this fact the best.

Unfortunately, this change makes impossible to "weave expose"
when weaver is not running.

plugin/net/cni.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"net"
 	"os"
-	"syscall"
 
 	"github.com/containernetworking/cni/pkg/ipam"
 	"github.com/containernetworking/cni/pkg/skel"
@@ -100,12 +99,11 @@ func (c *CNIPlugin) CmdAdd(args *skel.CmdArgs) error {
 				return fmt.Errorf("unable to allocate IP address for bridge: %s", err)
 			}
 			bridgeCIDR := bridgeIPResult.IPs[0].Address
-			if err := assignBridgeIP(conf.BrName, bridgeCIDR); err != nil {
-				return fmt.Errorf("unable to assign IP address to bridge: %s", err)
-			}
-			if err := weavenet.ExposeNAT(bridgeCIDR); err != nil {
-				return fmt.Errorf("unable to create NAT rules: %s", err)
+
+			if err := c.weave.Expose(&bridgeCIDR); err != nil {
+				return fmt.Errorf("unable to expose bridge %q: %s", conf.BrName, err)
 			}
+
 			bridgeIP = bridgeCIDR.IP
 		} else if err != nil {
 			return err
@@ -167,22 +165,6 @@ func setupRoutes(link netlink.Link, name string, ipnet net.IPNet, gw net.IP, rou
 	return nil
 }
 
-func assignBridgeIP(bridgeName string, ipnet net.IPNet) error {
-	link, err := netlink.LinkByName(bridgeName)
-	if err != nil {
-		return err
-	}
-	if err := netlink.AddrAdd(link, &netlink.Addr{IPNet: &ipnet}); err != nil {
-		// Treat as non-error if this address is already there
-		// - maybe another copy of this program just added it
-		if err == syscall.Errno(syscall.EEXIST) {
-			return nil
-		}
-		return fmt.Errorf("failed to add IP address to %q: %v", bridgeName, err)
-	}
-	return nil
-}
-
 // As of CNI 0.5 spec:
 //   "Plugins should generally complete a DEL action without error even if some resources are missing"
 // this method should therefore return nil in most, if not all, cases.