Networking:  Improve the network device registration logic.  When multiple link types are used, modify how each interface number is assigned to the device name by incrementing the device number individually for each interface link type.  From Max Neklyudov.

PIC32MZ: Fix some repeated typos and work around an issue with passing defined parameters to a macro that takes multiple parameters

PIC32MX/Z: Partial review of PIC32MZ cp0 register -- need to do more; Also found issues with definitions for PIC32MX -- need to be retested

PIC32MZ: Add file for GPIO interrupt support.  There are issues so configuration is EXPERIMENTAL for now

Extend the fd_set type definition so that it can handle more than 32 descriptors (if so configured).  From Max Neklyudov

Fix places where the errno value was being overwritten by subsequent actions so that the returned errno value was incorrect.  From Max Neklyudov.