Recent STM32 UART change:  Wasn't that logic backward?  Shouldn't that have been disable the USART if (1) we don't have than many USARTs OR (2) we don't have that particular USART -- not AND.

STM32 F401:  Only 3 USARTS, but need to set STM32_NUSARTS to six because they are not numbered sequentially

wdog.h does not contain any application interface, only internal OS interface.  Further, it is non-standard.  Move wdog.h from include/ to include/nuttx. For the same reason, move the description of the watchdog timer interfaces from the Users Guide to the Porting Guide.

If we run out of pre-allocated watchdog times, the logic will allocate additional timers from the heap.  A reserve of pre-allocated watchdog timers is maintained so that there will always be timers available for interrupt handlers.

ARP reuestion logc needs to do the right thing if (1) the address is a broadcast or multicast address, and (2) if the IP address lies outside of the network.  Thanks to Manuel Stuehn

ARP: Add signal logic so that we do not have to wait so long with the network responses to ARP requests quickly

Move some internal networking function protoypes out of the public include/nuttx/net/arp.h into to the private net/arp/arp.h