include/nuttx/net/netdev.h and several Ethernet drivers in arch/: Most...

include/nuttx/net/netdev.h and several Ethernet drivers in arch/:  Most network drivers to not support statistics.  Those that do only support them when DEBUG is enabled.  Each driver collects an architecture specific set of statistics and there is no mechanism in place to view those statistics.  Thus, the driver feature was mostly useless.  This change standardizes the driver statistics and puts the definition in the common network device structure defined in netdev.h where they can be accessed by network applications.  All Ethernet drivers that collect statistics have been adapted to use these common statistics.