Add description of the CTRL_MAC_ADDR feature bit
Add support for the EVENT_IDX feature to the network driver

This allows the driver to defer the Tx completion interrupt.
Fix setting of the Rx filters

QEMU 1.4 made the descriptor requirement stricter - the size of
buffer descriptor must exactly match the number of MAC addresses
provided.
Minor changes to the multiqueue driver

  - Fix statistics bugs
  - Add couple of asserts
  - Remove unused typedef