runtime: add the mtu support for updating routes

Some cni plugins will set the MTU of some routes, such as cilium will
modify the MTU of the default route. If the mtu of the route is not set
correctly, it may cause excessive fragmentation or even packet loss of
network packets. Therefore, this PR adds the setting of the MTU of the
route. First, when obtaining the route, if the MTU is set, the MTU will
also be obtained and set to the route in the guest.

Signed-off-by: Fupan Li <fupan.lfp@antgroup.com>

src/runtime/virtcontainers/network.go

@@ -310,6 +310,8 @@ func generateVCNetworkStructures(ctx context.Context, endpoints []Endpoint) ([]*
 			r.Scope = uint32(route.Scope)
 			r.Family = utils.ConvertAddressFamily((int32)(route.Family))
 			r.Flags = uint32(route.Flags)
+			r.Mtu = uint32(route.MTU)
+
 			routes = append(routes, &r)
 		}
 

src/runtime/virtcontainers/pkg/agent/protocols/types.pb.go

@@ -308,6 +308,7 @@ type Route struct {
 	Scope   uint32   `protobuf:"varint,5,opt,name=scope,proto3" json:"scope,omitempty"`
 	Family  IPFamily `protobuf:"varint,6,opt,name=family,proto3,enum=types.IPFamily" json:"family,omitempty"`
 	Flags   uint32   `protobuf:"varint,7,opt,name=flags,proto3" json:"flags,omitempty"`
+	Mtu     uint32   `protobuf:"varint,8,opt,name=mtu,proto3" json:"mtu,omitempty"`
 }
 
 func (x *Route) Reset() {