Rename virBandwidth to virNetDevBandwidth, and virRate to
virNetDevBandwidthRate.

* src/util/network.c, src/util/network.h: Rename bandwidth
  structs and APIs
* src/conf/domain_conf.c, src/conf/domain_conf.h,
  src/conf/network_conf.c, src/conf/network_conf.h,
  src/lxc/lxc_driver.c, src/network/bridge_driver.c,
  src/qemu/qemu_command.c, src/util/macvtap.c,
  src/util/macvtap.h, tools/virsh.c: Update for API changes.