make the driver configurable for various targets, and a small bug fix

- CONFIG_NO_TIMESTAMP removes timestamp field from each packet header
- CONFIG_NR_PORTS defines the number of ports supported
  (if 1, no port multiplexing is conducted at every packet)
- so for an experimental DMA testing,
  make CONFIG_PHY_INIT=y CONFIG_NO_TIMESTAMP=y CONFIG_NR_PORTS=1
- a bug fix for netif_napi_del/disable, putting from nf10_remove to
  nf10_down.
add NAAS flag in Makefile to make an experimental driver

- The experimental driver is for out-of-tree DMA.
- add FIXME, TODO labels for things that should be done after
  interrupt control of nf10 is changed in an explicit way.
make lbuf_rx configurable w/ CONFIG_NO_TIMESTAMP and CONFIG_NR_PORTS